You can also update the front end, but leave the bike at stock height. You can do this with spacers in the dampers of cartridge forks. Then do the other work as finances allow.
I put a YZ250F KYB 48mm fork on my bike. Documented here...
Here's the write up in Pipeburn https://www.pipeburn.com/home/2012/12/5/1986-bmw-r80rt-bopper.html
It's had a few changes since then. I think Michael is going to reduce the front back down to a 19" wheel.