" what shall I get as an second bike - one to work on while ride the other one?"
NOW there is a loaded question. What do you dream of owning? Motorcycle preference is an individual thing, kind of surprised you'd ask.
If I was not income challenged, a bunch of exotic machines come to mind, Financial freedom sure could be fun.
As a thrifty person, I have never hesitated to seek out useful old technology, so some older motorcycle options come to mind. the good news is that there are some excellent bikes languishing in garages of individuals who simply got bored with them or just don't ride much. This is how I got my G5 deluxe.
I am always interested in learning of old BMW AIRHEADS, MOTO GUZZI's, DUCATI's standing idle. I even like URALS. Some years ago I was GIVEN a BSA A65 LIGHTNING because it no longer ran, & the owner needed the space.
BMW is a very practical way to go, they are excellent machines, & most airheads are still running. They can be set up to Tour, Cruise, or Race. Enclosing pix of 2 that I built.
*The big Black & White 1964/2 is a 900cc conversion with later wheels engine & drivetrain.
*The Florida Green 1972/5 750cc was sold by a vintage racer, it finished 7th in the battle of the twins at Daytona- not very competitive, but a pleaser on the street.
You should follow your heart & ask around, you never know what may turn up.