The questions become, (a) "Why do you want to interface via RS232 at all?" (b) "Why do you want to use RS485?" (c) Why are you opposed to USB?" (d) "What difference does it make that USB is half-duplex, when it is 100x fast enough to send every message separately?"

There are, surely, good reasons why these questions arise, so there must be good answers. If (a) is because you have external devices that already use RS232, then that's one good reason. However, I've seen no justification, yet, for RS485, as opposed, say, to RS422, which is very similar.

Which features of these standards work or don't work for you?

Are you just exploring possible scenarios? What are you REQUIREMENTS? Those are criteria without which the system cannot work. Things that would be "nice" or "easy" don't necessarily fit.

RE