The bugs that you're going to experience in CK2 are most likely not going to be technical glitches physically preventing you from playing. Exceptions do apply, there certainly exist people who can't play the game at all or play it stably in certain versions, but I think that's rare. And I've almost never experienced anything like that myself, far less often than with most games. I think as regards technical bugs that 'physically' crash your game or corrupt your save are rare. From my own personal experience, they are practically nonexistent and whatever little is left is not worth complaining about. (Especially considering that a CTD has a good chance of being caused by something in the system or drivers, not just the game you're playing.)
So if the above are bugs you worry about, then you can safely stop worrying about them. In my >2000 hours of playing CK2, I can recall maybe one instance (and that was actually 2.3.3, the supposedly very stable version) where I got my two most recent saves corrupted and had to go back to a slightly older one (yes, keep saving every couple of years, not just autosave, but this is a basic precaution with every game). Maybe a CTD or two in 2012-2013. I don't even remember. So don't worry.
On the other hand, the game is literally full of bugs (not always fulfilling everyone's definition of a bug) that disturb the proper functioning of certain mechanics. There are also quite multiple examples of questionable logic in the game's events and design/balancing decisions, of which the quality has been deteroriating over the last year or two. When a patch is released, there are almost invariably some new bugs and flaws introduced the game as a result. There is also typically frustration about some bugs and flaws not being fixed or only being fixed partially or being fixed in a band-aid kind of way (provisional fix that is not an elegant solution) or being fixed in a way that doesn't really fix them or causes some other issues. The speed with which such issues are then fixed varies, and there are complaints among fans that Paradox 1) is not reacting fast enough and 2) not seeming to
take the problem seriously enough. I'm not inside anybody's mind, but judging by the results and some of the conversations/PR material, I definitely agree with #2 and mostly agree with #1 — there have been examples of fast response in the past, although not recently that I'm aware of. In any case, there is most definitely a serious problem with this king of bugs that isn't getting any better and isn't taken seriously enough. The game also contains a lot of issues that would normally be considered bugs or at least flaws, but there is — has been in the last year — a growing sentiment of defensiveness concerning them, with an attempt to redefine them out of existence. The situation used to be better in the past in this regard, so maybe it'll go back to closer to normal with time, eventually.
TL;DR: If you can't live with technical issues but can live with feature bugs and flaws, then you probably won't have a problem (as a seriously disappointed customer for other reasons, I confirm that the
stability and compatibility of the game is most splendid and performance issues aren't that bad even on my aged Core 2 Duo PC). However, if you can live witch technical issues but can't tolerate too many feature bugs and flaws in a game that don't get much attention in terms of fixing, then you're going to be disappointed (I certainly am).
The most current version is the most stable I've seen ever for ck2. The nagging most mentioned bugs are really not that big of a deal, they are only an issue because they've been on the fix it list very long is all. Their level of importance or effect on your average player is very minimal. I hate this, but the most fun/reliable game to be had out of ck2 requires all the major dlc's sadly. I really hate this model but I recently bought the last two against better judgement and discovered the game plays better due to the missing events now firing that were flagged for the dlc's. Its best to wait for the spring/fall sales for steam cause paradox titles go on sale dramatically and you can pickup the base game+all priority dlc's for the price of a normal fully patched non paradox game. (its sad that you have to wait for sales to buy paradox's overpriced product model)
I don't mind the need to pay for DLCs but I greatly do mind the non-working features or missing/disturbed realism or immersion and the apparent lack of commitment to getting it right. But it depends where you are in your life, I guess. I've been over 30 for a while, with a job that tends to pay and no wife and children to support, so I'm more protective of my time and attention span than my wallet. Some ten years ago, I'd have had more time but a tight budget and not even a credit card to begin with, so that would have led to different perceptions perhaps. But in any case, I strongly suggest getting the DLCs earlier than later just to be done with it and not limiting your full enjoyment of the game. If money's a bit of an issue, maybe save on songs and unit models, as while they are great
enhancements, their
absence won't be felt. Maybe don't get The Republic if you aren't going to play as a republican character, don't get Rajas of India if you aren't planning on playing in India, don't get Sunset Invasion if you don't want Aztecs landing in Europe with an invasion, don't get Sword of Islam (one of the only three DLCs I don't have) if you aren't going to play as a Muslim.
And, budgeting-wise, you can always delay playing in India or a Muslim or as a Patrician. On the other hand, you want to get The Old Gods, Charlemagne, Sons of Abraham and (especially, due to retinues) Legacy of Rome due to the mechanics that affect your whole game. Maybe spend an hour researching Way of Life before purchasing.
But in any case, if you can just take 1-2 more hours at work rather than spending 1-2 hours of your (actually very precious) free time trying to decide whether you should purchase a DLC or not, then just take the overtime and spend the money on the DLC without the to-buy-or-not-to-buy kind of headache. I found this out the hard way.