Noe of them really conlict with each other, however most of the time each module is relativly seperate from each other. You can play basicly any module independantly and you aren't losing many features. For example: The fishing and sushi expansions can used as just adding a single set of features. However if you also have VE:Mechanoids you can also get a fish factory, or honey from VE:Vikings can be used for desserts in VE:Culinary.

The features of many different modules can act upon other modules can work with other modules, however playing the independantly works just fine.

Some of them have specific time periods in mind, but you can have them all enabled and just turn off factions that don't fit your theme if you like. I keep vikings on 24/7 for beekeeping and usually have the faction turned off.