Hi @KtDunster
Welcome to the Sonos Community!
Question 1: Can I plug multiple analog sources into a Sonos system?
Yes, but each device will only accept one input each, unless you use a third-party switch of some kind.
You can have multiple speakers equipped with Line In connected to multiple input sources and they will all be available to all Sonos rooms in the app.
Question 2: If not should I still get a Sonos Amp?
Like all the others, Amp has one Line-In input. It sounds good though, so if you have some passive speakers already, sure.
Question 3: If not should I get a Play:5 Gen1 for the turntable - if so can I still listen to vinyl on other speakers in other rooms?
In short, no. Play:5 Gen 1 does not support S2 software (which your Play:1 is currently using) and moving to S1 would restrict your future options. If you’re after a second-hand speaker, I recommend avoiding Play:5 Gen 1. Play:5 Gen 2 speakers are preferable over Gen 1, but I would not be surprised to hear if you could get a brand new Era 100 plus a Line In adaptor for less. The Sonos Five is our current equivalent offering.
As mentioned above, any (Line In) source connected to a Sonos product can be played in any Sonos room.
Streaming music services are not going to be a problem, and playing your own music stored on a Mac will be fine too. The only way to play music physically stored on an iPhone/iPad is to use AirPlay - for AirPlay to be played to a Play:1, the Play:1 must be grouped with another (compatible) speaker which is the AirPlay target. All our current speaker models support AirPlay (if looking at second-hand speakers, look for touch-sensitive controls - any speaker with these will also support AirPlay). Era models also support Bluetooth.
I hope this helps.
"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein