As long as they continue to work, you’re fine. You won’t be able to use them as surround speakers in a Sonos home theater setup, but other than that, you shouldn’t have issues. I prefer a stereo pair over a single speaker anyway. 

I’m new to this forum and I’ve been reading some related topics. Sounds like I should sell my pair of gen 1 Play 5’s and buy a pair of the Play 1’s. All agree?

Not sure why you need agreement from anyone else. You’re the best judge of what your ears prefer, and what your finances can afford. A pair of Sonos Ones is certainly a great starting platform, but the again, so is pretty much any Sonos speaker. Although I wouldn’t start with a Sub, as it needs a regular Sonos speaker to be bonded to.

I sure don’t think swapping a pair of Play 5s for a pair of Play 1s or Ones is a good trade when thinking about sound quality.

A pair of Ones or One SLs and a Sub maybe, but you said limited budget and the Sub comes dear.

My thought is to sell the pair of gen 1 Play 5’s and get a pair of the Sonos ones (gen 2). Which pair would sound the best by adding a sub?