Best Countries for Beginners
USA would be the easiest. All the resources you could ever want, large educated population, and nobody can touch you militarily.
Cuba has everything you need, slavery and abolationism. Iron, coal and wood to try industrialization. Arable lands if you want to go sugarcane plantations.
Fight for independence against Spain. No one cares about you, so you are pretty safe, but you can expand to weak neighbors if you want to try wars and naval landings. And it has only one province and super easy to manage.
Russia would also be a decent one. Large army to discourage people attacking you. Plus some early conquest if you are looking for it.
It also has most of the resources internally build your economy. Other then rubber, but will that is what colonization/armies are for.
Downsides being it has crap tax laws, and starts with serfdom which blocks improving some laws on the economy. But you can work to get rid of that over time.
I got lucky since passing establishing a Dedicated Police Force made my land owners faction happy enough that I could pass Serfdom Abolished without making them radical. Which also lowered their political power (since serfdom gives a +50% modifer to landowner political strength).
So a lot of early game was improving economy while weakening the Landowner faction over time mostly by getting rid of laws that gave them political power bonuses.
Hindsight I should have gotten rid of the Tsar earlier (since he was in the landowners party).
Portugal is a good choice. Small, safe, and has colonies for raw resources. You can definitely specialize in a couple of trades as Portugal with a chill game, not having to worry about military, except if you wanna use your starting military to kill natives.
Thailand / Siam
I liked to play Siam first because it’s an isolated economy with no trade routes and very hard to change this law and it basically teaches you which buildings you need to build to get the right ressources to increase your GDP and make your people happy while you are also able to have some small wars to annex the small countries in your reach of power.
If you finally get out of your isolated state you will very quickly find out how much trading goods can change your whole income and even bring you to bankruptcy if you aren’t careful.
It also teaches you the political basics and that you definitely don’t want to piss off the main political power in your country because this will lead you to endless revolutions and civil wars.