It seems to me that interstellar trade -- with or without FTL -- is quite unlikely. I wrote some thoughts on this about a year ago, (https://one.mikro2nd.net/2021/07/interstellar/) but tl;dr: If your society is capable of marshalling the resources/energy necessary for interstellar travel in the first place, you have most likely, of necessity, solved the problem of getting more resources. War seems slightly more likely because "ideology".

Ultimately I think my notion is quite similar to yours: that the primary exchanges would be culture (art, music, fashions, language, rites,...) so the things for which we want "communication".