Yes, that should be possible without any problems. https://en.community.sonos.com/speakers-2.... Of course, you need a suitable preamplifier for the turntable, as the Sonos devices only have line-in. You don't need any Sonos ports in this setup.

Good morning

You can only connect one device to the port. So if you want to use CD and PS, then a double cinch (Y) connector on the port could be the solution: https://www.digitec.ch/de...

This has nothing to do with the speakers.

I understand that you want to use your old collection. But maybe a digital collection would be easier. Sonos not only supports Spotify: https://support.sonos.com/de-de...
In addition, the connection via RCA (analogue) is only a makeshift solution in terms of quality.