Recent air combat sim recommendations?

I think most here would recommend running the standalone version because you get new modules sooner. I think Steam is still missing some modules too. :)

Module transfer, the method of transfer from Steam to standalone varies depending on when the module was released as they changed protection from Starforce to Steam key on 12 May 2017.

So anything released on Steam after that date can be brought over automatically, just go to your DCS profile and bind your Steam account there.

Anything released on Steam before that date requires a more manual process.

The faq covers most of it: Steam

Multiplayer I’m not sure about, but what you said sounds correct.