Krakow is pretty easy because you'll always have a great power ally with their armies right on the border of whomever you decide to sic them on next. it's just memey because you bounce around between them and have them tear each other apart for you
any country is playable, though. here's my Sulu -> Malaya game :) (I got cucked on the button to become Indonesia because you can't do it if the Netherlands has already organised it. A shame because that would have been a lot of accepted pops but I like the colour of Malaya anyway :)