There's hypothetically a bunch of different version of communism for everyone. The thing is, Marx described the problems with capitalism, and some vague sense of what socialism could be, some guidelines of what it should aim for, then kind of left the details up to each individual society to get there how they think is best based on their individual material conditions. He gave his own guesses, but didn't think he could predict that part fully, it would be up to the people of the future to figure it out and build on. A third world country, rural serf based near fuedal society, like Russia, would have completely different needs from some post-industrial country, like if Germany turned communist, for example. If the world's sole superpower, the US, turned communist, it would probably be a lot different than communist countries that had to transition under siege neighboring imperialism, like Cuba, North Korea, or Vietnam.

This is just to answer your last question. Don't think this really addresses your other questions, but just wanted to explain that part, as I've had it explained to me before. But I generally agree with you. There should still be some form of democracy but it might look different than what we are used to here in the US or liberal west.

Its called worker lead, classless society.

foss has a legally binding licence to support itself, this licence can be seen as a vanguard as it steers and protects the software, without the licence people would be sure to steal and monetise others works. But let's say Foss became the defacto, everyone releases free fully open and no anti feature software, we could loss the vanguard and naturally a classless system would be present.