Re: 650c tires vs 26"
Due to the weirdness that COVID put on the open market, you may find a lot of changes to what you can or cannot buy for your trusty Corsa.
Back to your question...I still run the 650c tires on my Corsa. I have been using Continental Gator Skins and like the performance and the ride. OTOH, I stocked up on tires a two years ago and still have new ones in my shop. I don't know what is available at this time in the 650c market.
I did convert a 650c RANS XStream to 26 (559) a few years back for a friend. He wanted a perceived larger tire selection of tires. On my XStream, I run 26 inch wheels...but as you can guess, I'm running Gator Skins on that also.
So, to wrap this up, in today's market, I'd look at the availability of 650c tires and see if you can find what you want. I think I'd stay at 650c for the time being unless you have something else driving your decision.
Steve / Bentrider28
2008 V3 steel
2003 Corsa (Steel)
2001 V-Rex S&S Coupled