Hello Keith and welcome
Your history is kinda similar to mine. I had a Z1000 MkII when I met my misses (at the time) which I sold to pay for our wedding and bought mu first 750 twin.
I don’t think you will go far wrong with a twin as a retirement project. I’m not quite at retirement stage yet but have 5 in my garage so far. Yes it is full so I now have plans for a 2nd even bigger garage. Mine are the CSR version (M model)
There are a few knocking about at the moment but think they are the next big project as they can pull £2500 to £3000
Most parts are still available so whatever you pick up will be doable one way or another