So, I started a new game of Stellaris with a few light mods. I have some time on my hands, about 14 days. Despite playing Stellaris for over 600 hours, I've never finished a full game. With that said, I'd also like to dive into EUIV at some point. I did play EUIV briefly in the past, but I never truly grasped the game's deeper mechanics. Fourteen days seems like it could provide a foundational understanding of EUIV. Who knows, EUIV might become my new favorite game, especially considering the vast amount of content available for it. On the other hand, Stellaris feels like comfort food; I can relax while building up my space nation. In my quest for an answer, I'm once again turning to the brilliant minds on Hexbear to assist me.
Sorry, I was doing a bit.
Here's an actual answer now that I am back from the store. Eu4 is a complicated game in the sense that it is archaic (released in 2013 (Ancient times)) and is suffering from serious powercreep and feature bloat from the last 10 years of shifting development. Some DLC contain quality of life features and essential mechanics, for example, automatic exploration of the world is locked behind a DLC, requiring the player to otherwise manually click each province to explore it.
Country recommendation, the ingame country picker has in-built recommends in it, if you for some reason have Domination installed, don't play the Ottomans, cause afaik they are now quite difficult to play with the new decadence mechanics. Otherwise, France, Spain and England are solid choices, plenty of content and powerful enough for anyone to do well with. For more confident players, I'd say Austria, Brandenburg and Florence are all fun, depending on if you want to do diplomacy, conquest or economic expansion respectively. If Europe bores you, you can play the Bahamani's in India, the Ming in China, Korea in Korea or one of the Japanese Daimyo, the Uesugi (well, the one with the 3 provinces in the middle of the main island) is a good starter pick for that place. If you are again feeling confident, doing Jihanzhou to Manchu to Great Qing is a fun game.
As for that blabber about the early modern period, that's just the general definition of the entire time period of EU4, not medieval nor entirely modern, but something in between.
Also, don't be afraid to look up console commands, the game can be excruciatingly unfair at times and to get myself through the first 1000 hours I utilized cheats extensively, now I can play confidently at normal difficulty without touching the | key.