Sorry for the late answer. I don't got a lot of time these days.
Long answer: Your question is not meaningful without specifying the measure of complexity.
Well, then let me play my "courts, factions, nobles"-mindgame and make up a situation to provide us with an example of the complexity I have in mind. Let's just assume you're in charge of the kingdom of Bohemia. The year is 1550, you've lost Silesia to Poland.
EXTERNAL AFFAIRS
You're currently at peace. You've declared Austria and Poland as your rivals and you're allied with Saxony. Your confession is catholicism. That's about all we need to know for now.
INTERNAL AFFAIRS
Your kingdom comprises 7 provinces, in each of which there is a "nobleman". The provinces and noblemen are attributed to three parliaments: Moravia, Bohemia, Lusitania. Here is a hypothetical list of parliaments and noblemen, showing their opinion, their factions, their rank etc.:
Bohemia
parliament
protestant / opinion -20
power balance: high aristocracy 7 : 18 local nobles; (based on the rank of the nobles; each region has 6 points)
confessional structure: protestantism 20 : 5 catholicism (based on confession of high aristocracy and local nobles, multiplied by rank)
confessional law: ?
taxrate: ?
noblemen
region "Bohemia": Wenzel of Rosental / rank 3 / catholic / anti Austria / leader of patronage faction Rosental / ADM 3, MIL 1, DIPL 5 / opinion 50
region "Erz": Veit of Kaunitz / rank 2 / catholic / anti Austria / patronage faction Rosental / ADM 3, MIL 6, DIPL 5 / opinion 60
region "Böhmerwald": Otto von Sternberg / rank 2 / protestant / anti Austria / patronage faction Lobkowitz / ADM 1, MIL 5, DIPL 1 / opinion -20
Moravia
parliament
protestant / opinion -40
power balance: high aristocracy 5 : 7 local nobles
confessional structure: protestantism 12 : 0 catholicism
confessional law: ?
taxrate: ?
noblemen
region "Ratibor": Max of Collalto / rank 1 / protestant / anti Austria / patronage faction Lobkowitz / ADM 2, MIL 6, DIPL 2 / opinion -40
region "Moravia": Franz of Lobkowitz / rank 4 / protestant / anti Poland / leader of patronage faction Lobkowitz / ADM 1, MIL 4, DIPL 4 / opinion 5
Lusitania
parliament
protestant / opinion -30
power balance: high aristocracy 3 : 12 local nobles
confessional structure: protestantism 12 : 0 catholicism
confessional law: ?
taxrate: ?
noblemen
region "Upper Lusitania": Adam of Tschernin / rank 1 / protestant / anti Poland / patronage faction Lobkowitz / ADM 2, MIL 1, DIPL 2 / opinion -30
region "Lower Lusitania" Franz of Slavata / rank 2 / protestant / anti Poland / patronage faction Lobkowitz / ADM 2, MIL 2, DIPL 4 / opinion -10
Your aulic council
Let's assume that you've maxed out your council for diplomatic affairs. For this purpose, you've appointed but ONE man as your councillor (in order not to dillute his skill by other advisors), namely Wenzel of Rosental because of his DIPL-skill of 5. This singulary position gives a huge opinion boost to Wenzel Rosental, but makes other nobles (especially those of higher rank, i.e. Franz of Lobkowitz) see him as your favourite (--> opinion malus).
ANALYSIS
You have very strong parliaments (the power balance parliament-noblemen favours parliaments)
You have a major confessional problem: all your parliaments are dominated by protestants, which is also why the relations tend to be very bad.
The two diplomatical factions in your country have about the same power (anti austria 8 : 7 anti poland); however, there is (by hazard) a quite significant connection between the anti-Austria and the catholic faction; and the anti-Poland protestant faction
MIND GAME
So, now that we know about the situation of your country, let's add some developments or decisions and take a look at the complexity of the options. Let's assume that you, as the king of Bohemia want to recapture Silesia from Poland.
Option: Declare war right now!
What would happen if you act immediatly, without considering the situation in your realm any further?
Declaring war against Poland will make the opinion of the Anti-Austria faction drop, which comprises the following noblemen (rank / opinion):
Wenzel of Rosental / 3 / 50
Veit of Kaunitz / 2 / 60
Otto of Sternberg / 2 / -20
Max of Collalto / 1 / -40
As your relations with the higher ranking noblemen are quite good (mainly due to Rosental and Kaunitz belonging to your confession), you don't need to fear any considerable collective resistance. The protestants Sternberg and, especially, Collalto will get quite upset. But the latter has no real influence anyway (rank 1). What is more of a problem, however, is that these two guys, Collalto and Sternberg, are two of your most talented generals (MIL 5 and 6). Now that you've totally let them down, you can't count on their skill in the upcoming war. Overall low opinions in half of your realm due to the confessional divide severely reduce your pool of competent personell. This mechanism would give you a real reason to establish confessional unity.
The relation with Rosental will suffer extraordinarily. Why? Because he is member of your aulic council and he is part of the anti-Austria (i.e. pro-Poland) faction. By acting against his interest
as a councillor, you will dissappoint him, which will result in a big opinion malus, which in turn reduces the skill that he "uses" in your favour. This should actually interest you. For example, you could use a diplomat in order to keep another faction from entering a war for a certain time – the better the skill of your diplomat, the more likely it is that he will be able to keep the faction out of the war. Of course you could just kick Rosental from the council and replace him with an anti-Poland nobleman, but this would be quite problematical since there are no catholics in the anti-Poland-faction, and appointing a protestant will surely cause a lot of trouble/alienate all catholics! Moreover, kicking a councillor is usually seen as an absolute eclat, not only for Rosental, but also for the anti-Austria faction. So let's not forget that Rosental is the second most important person in your realm, not necessarily a favourite, but the second highest noblemen in your realm, most important nobleman in the catholic faction, leader of a patronage-faction and your single councillor. In this position, you should think about how you handle him.
Apart from the effects on noblemen, you will also have to consider a second big question: where do you get the money from that you need for your war with Poland? Since your noblemen are not very powerfull (overall low ranks; --> power balance in favour of the parliaments), and since the noblemen in Bohemia have no interest in a war against Poland anyway, you will have to occupy yourself with the parliaments. Wouldn't be much of a problem, if it wasn't for the confessional issue. ALL your parliaments are dominated by protestants. In other words: except for a few catholic noblemen (the elite you have to count on but that you've just alienated with your war against Poland), your whole realm sticks to the protestant confession.
Naturally, this means that implementing taxes for an aggressive war will be costly. Protestants will use your weakness and demand concessions in return for money. How is this modelled in the game? Quite simple. Demanding taxes while the parliaments' opinion of you is low (due to their confession), and under unfavourable circumstances (aggressive war*) will lead to resistance if you don't offer something in return. For example, you could make confessional concessions and change the confessional law in the parliaments in favour of the protestants. Or you could reduce the ranks of noblemen (especially the catholics) to please the parliaments. If you don't do that, you might face a "rebellion" by the estates. Pretty much the worst thing that could happen to you, especially since there are hardly any noblemen left that you could still count on, now that you've just let down your loyal catholics who are all part of the pro-Poland-faction.
Making concessions to parliaments should have consequences as well. By giving in to the demands of the estates in order to finance your war, you will loose prestige, and your reputation with all the catholic noblemen and ideally also with the pope and other catholic monarchs will suffer. Moreover, since prestige is a factor in your "court/pomp/ceremony"-pool of royal graces, your court's attractiveness will suffer as the balance of power shifts from the crown to the estates. This means that you will have less means to manipulate noblemen, which in turn means that you won't be able to use them to influence the parliaments.
To sum it up: In the current situation, an aggressive war against Poland would be quite dangerous, but not impossible. For example, you could still hire commoners to be your generals (as you don't have any competent nobles willing to serve you), but this will upset all nobles in your realm. Baiting the protestants could even be part of your plan. You could try to get them to rebellion in order to beat them down once and for all. This can be an option as well, but in this case, you better have a strong ally to help you (for this you also need a good diplomat in your service), and you better make sure that Poland is not too much of a threat. If you succeed in beating down a major revolt of the (protestant) estates, you've probably done a big step into the direction of confessional unity, as you will be allowed to replace the rebellious noblemen with loyal catholics.
* Now that I think of it, this could be another task for your diplomats: influencing the perception of a war. A good diplomat could actually make your parliaments and nobles support your war. Using diplomatic agents for negotiatons with the parliaments and other noblemen would be a nice and immersive touch!