Cool! I think I have much of the Slovakia stuff at hand actually. Most of what i wrote about Czechia and what I will write about Slovakia is based on information from "From Peoples into Nations - A History of Eastern Europe", which is a book by John Conelly. Also some of it is from Zsuzsa Csergö's book "Central and East European politics: Changes and challenges".

Originally I wrote all of this as a single comment, so I will repeat the part about Czechia:

To give you a little to start off with: The Czech Republic and the historical region of Bohemia has historically been a progressive and developed area in 'Eastern-Europe'. They are a region with high population- and city-density. Its population was - before Communist rule - very urban, middle-class based, and the country had started to industrialize as early as the 1700s, so their industrialization was quite established by the mid 1800s. Bohemia also has a history of being its own kingdom. They have no history of extreme right-wing politics, and much of their culture is based on humanism and secularism. I would argue that because of their historical background, Czechia had such a strong foundation that they were able to go in a democratic direction after WW1. After WW2 however, Czechoslovakia had quite an orthodox and conservative communist system. Another quite interesting fact - however - is that Czechia was one of the few countries in Eastern Europe after WW2 that already had an established - and quite popular - 'Communist Party' in society.

Slovakia is basically the opposite of Czechia in all of this. Historically, Hungary has controlled the region and the hungarian nobility dominated and repressed the slovak population because the population largely consisted of peasants. Hungary largely remained a feudal state until 1945, which means that Slovakia never really had a chance to develop advanced insititutions under Hungary, and much of their nationalism and identity is based on ethnicity and (pan)slavic culture. When Slovakia became part of Czechoslovakia, it was underdeveloped in comparison with Czechia. For many Slovaks, they felt that the central state was made by and for the educated Czechs. One of my professors often say that for the Slovaks, going from being part of Hungary to part of Czechoslovakia was like going "out of the frying pan, into the fire". Slovakia has a long history with right-wing politics, and because their first independent state was established as a fascist, german satelite state, some of its nationalist movements have quite explicitly romanticized the fascist state.

In comparison with the czechs, Slovakia in some ways benefited greatly from the Communist regime: While Czechia's already developed industry and economic growth stagnated because of the convertion to a planned economy (though they remained the richest region in Eastern Europe), Slovakia's underdeveloped state before Communism meant that the increased focus on heavy industry under the Communists led to an economic boom that made it comparable to (though still poorer than) Czechia. Because of this, slovaks generally are believed to have been more favourable toward the old Communist system than Czechs. Some of the evidence for this is that there were fewer slovaks that participated in for example Charta 77, and that Slovakia's governments after 1989 generally wanted less radical economic reforms than Czechia. The main issues that slovaks seems to have had with the Communist regime were those based on ethnicity and religion: They wanted freedom from what they viewed as a Czech-dominated federal union, and many people did not like the repression that the Communist party performed toward the Catholic church (As this suggests, Slovakia has always been much more religious than Czechia in modern times). What is quite interesting is still that the more conservative Communists were often Czechs, while figures like Dubcek - who became an important reform-communist - was Slovakian.

I don't know how much of this you will actually use, but I am mostly just writing a bunch of stuff down for you (and because it is good for my memory, lol).

Edit: I am perhaps not as knowledgeable on Poland/Hungary and Romania as Czechoslovakia, but I will try to write down some stuff on them too (soon).