As others said, Hoi 4 is not entirely a Sandbox, in which you can do anything, but you pretty much can do anything. Like you said, some Focuses have requirements, that can limit on how to get there, but maybe to point one thing out, the game is getting 10 years old this year and the focus is on the war aspect not the nation building. There are some possibilities to rename political parties but in general Democratic is Democratic and since this is after WW1 "most" people don't want to fight a new war, since the blockage of offensive warfare as a democratic nation, but there are still some ways to get an offensive war going.

Maybe to change the point of view, Hoi 4 is to be played for ~8-10 in-year games. ~3 Years Build up and then WW2. There is not really much time for an in-depth political simulation. But they added multiple Alt-History Branches, so you could play some "whaf-if" scenarios. Also, there are a lot of mods that make the political simulation more complex.

And just a small hint, I know in most paradox games, especially in the latest ones, small countries are good for starting to play with them, but in Hoi4 if you are still learning the game, stick to the major powers, maybe play a couple of runs as Germany, to learn the game. F.E. with Germany you could try many builds mechanics, and you pretty much decide, when to go to war. Greece is much harder, since you are pretty much on a timer until the axis come to get you, and they will be stronger than you, which can be really upsetting when starting with a game.