I have put 100 of hours into EU4 , Hoi4 and Stellaris without the need for DLC or additional “packs “
And $130 for a sloppy mess ..
To be fair, on the paradox forums, the common number for finishing the tutorial of EU4 is 500 hours. So, for 100 hours you really shouldn't need any other packs (especially as many important DLC mechanics such as government, extended diplomacy, and war rework have been added into the base game a few years after they came with paid DLC). The "need" for packs arises if you are looking for differences between the different parts of the world besides geography: thousands of region- or country-specific events, unique mechanics, playing non-monarchies, non-generic mission trees etc. I don't think these things are very important in your first 5 or so campaigns. But if you hit 20, you probably don't want to be playing with the generic stuff.
In your case, for example, you might want to play Scotland, which is fine in the base game, as it is in an interesting situation geographically and politically, and there is quite some thing to do. But wouldn't it be even better if you get unique missions to take over then British Isles with unique rewards? And use innovativeness (a DLC mechanic irrc) as a key distinguishing feature of your empire, while also working towards a wooden wall of ships around the isles? And get unique Scottish advisors and great people through historic events? There is an also a unique government reform iirc, and Edinburgh Castle as a wonder with 3 tiers that want to be built. Without these, the difference between playing Wales or Scotland isn't large, besides the initial situation for the first 20 or so years, as Scotland is stronger and can take out England quickly due to its alliance with France, while Wales is a bit more precarious. This is when the additional packs become interesting.
Yes, I sound like a PDX marketing person. But in my defense: I'll probably never play a single game for as many hours than I've played EU4, and even if I know that I've probably spend 500+ € on the game (over 10+ years), it feels good value, as it's not just quantity that I got, but many, many nice memories of interesting campaigns. It's probably also helped a lot by campaigns being more easily distinguishable than the ones in civ games, because I usually don't repeat countries in EU4, and if so, I have very different goals.