I've been working on Norwegian Wood for the past week and have tried many different approaches to the first 30-50 years. This is Ironman Hard/AI bonuses, so especially for this achievement I need a good early game or I won't be able to make progress quickly enough (I had one attempt stalemate once Muscovy started allying major European powers like England in the early 1500's).
Game Start
Joining the HRE is a great idea, which means I'll need +200 relations with Austria, so I'll want the +dip rep advisor to gain an alliance (+100 improve+guarantee+dip rep advisor is enough) -- I restart if one isn't available.
Day 1 ally Sweden and get Hansa to support independence. Declare independence on day 4 or 5, and I want to have a first king without horrible stats and ideally at least 2 adm and 2 mil. If I have this, I insult the Papal State on day 5 with my second diplomat so I can declare Restraint of Appeals. I'll be converting to Protestant later anyway, so for the first 50 years I'd prefer to have the prestige and minus unrest bonuses rather than a minor trickle of papal influence. Also, if you happen to get a Theologian at some point (and have the proper monarch stats) you can use Dissolution of the Monasteries for extra tax income. Following this, you'll be at war, so use your diplomats to improving relations with Austria and Poland. One minor thing, I switch my merchants to be collecting in both the North Sea and Lubeck at the start: the North Sea trade will predominantly flow to Lubeck even without your steering, so it's better to make extra money until you can dominate Lubeck sufficiently to make it worth steering it all there.
Independence War
My favorite approach is joining the HRE and reducing Denmark's provinces such that it can be vassalized in the next war. To join the HRE while still reducing Denmark's provinces enough to vassalize them in the next war, I take Fyn for myself, give Skane+Halland+Blekinge to the Hansa (be sure to siege these yourself before the Swedish do, so you can transfer ownership to the Hansa before you make peace), and cancel their vassalage of Holstein. The Hansa are a useful ally in the critical early game, and you can easily turn on them once Denmark is your vassal to regain the three Danish provinces and take Lubeck for yourself.
Next steps
When the war is over, core Fyn and ally+marry+guarantee+mil access Austria to join the HRE.
Muscovy and Sweden are your major problems in the early game. I think it's absolutely necessary to stop Muscovy's expansion by 1500 which is why I go for Austria and Poland+Lithuania as my two major allies. Even with them, fighting Muscovy+Sweden is a pain and it can be difficult to pull off much more than a white peace depending on how effectively your allies concentrate and kill enemy armies. I tried various approaches to attacking Novgorod to limit the amount Muscovy can take from them, but it's really the Muscovy+Sweden alliance that is the major problem. In my current run, which has been the most successful by far (early 1500's currently), I let Muscovy and Sweden 1/3 of Novgorod each without jumping in, and because they then had a land border Muscovy broke the alliance immediately. This fixed my problems because Muscovy even offered to ally me (I improved relations also) and helped me to focus on eating Sweden and vassalizing Denmark. Austria and Poland+Lithuania generally won't join offensive wars against Sweden due to distance and "attitude toward country" modifiers, so it's useful to have more help.
In the first war with Sweden I took four provinces in the west: Vastergotland for the port, Dalaskogen (copper mine), Lappland, and Halsingland. I also took Aland, Finland, Osterbotten, and Nyland to release as Finland. Immediately after, Hansa broke the alliance and went hostile, so I fed back the Danish provinces I gave them at the start (I vassalized Denmark as soon as the first truce ended, which was before the Swedish war), I took Lubeck, and I released Hamburg.
Then, around 1490 I had the opportunity to declare war on Muscovy and bring in both Austria and Poland+Lithuania, while they had no useful allies (Muscovy broke its alliance with me after my second war with Sweden in which I regained all of the Finnish cores+some they took from Novgorod, and another Swedish province). I walked over to Siberia with some merc infantry and stole their 80% colony to cut off eastern expansion, released Perm, and took 4 Novgorod cores to release (Muscovy had eaten Novgorod entirely by this point). I'm fighting my second Muscovy war now, around 1512, and it won't be long before they're effectively eliminated.
I also turned Finland into a march, which seems fantastic given their national ideas. I've been feeding them provinces in Estonia/Latvia (same culture group for them) and will probably keep it a march until I've dismantled Poland+Lithuania.
Idea Groups
I went Quantity, Exploration, Expansion. The order is just how it worked out due to monarch stats and because you'll be spending a fair number of dip points during peace negotiations and annexing Denmark. I thought about other military options, but I really think Quantity is best for Norway's position in the early game. Offensive's bonuses don't really kick in until you finish the idea group which is too late for the critical early wars against Sweden and Muscovy, Defensive helps early on but I wanted something that would boost my navy and give me manpower because even mixing in merc infantry isn't enough with the frequent wars (not to mention the +50% force limit allows me to maintain a decent sized army for once). Having 4 colonists is going to be very useful for this achievement I think; I've already bstarted colonizing Canada, so far uncontested (England has all of Ireland and Scotland as vassals but hasn't annexed them yet). My fleet limit is also +50% due to Quantity+Exploration; I'll probably go Maritime as my next diplomacy idea unless I pick up influence -- depends on how much more expansion through vassals I plan on doing.
England/Scotland/Ireland
You'll typically fight Scotland in early wars because they almost always ally Sweden, but I've found that taking provinces in this area just isn't worth it. You can't afford to piss off England while you're trying to deal with Sweden and Muscovy because it's impossible to match their fleet and you absolutely need your trade ships working in Lubeck to keep your income flowing. Also, even if it owns Ireland+Scotland, England will only have about half of the North Sea provincial trade value (perhaps less if you focus on building markets) and I've had no issue keeping nearly all of it flowing to Lubeck due to merchants from the northern German minors. Because I flipped to Protestant, I might even end up allying England, but there's really not much point in fighting them unless you plan to conquer the entire isles, and that's only possible much later when your force limits allow you to match them (due to their heavy ships, nobody will be able to land troops to help you fight unless you can beat their navy, and again not until mid-game is that possible).
