JH313,
I also have arthritis, osteo type with some RA thrown in for the past 30 years. I continue to build/fly and manage it with some powerful NSAIDs-Celebrex, etc. For the wrists/hands, I use a transmitter tray which totally supports the weight of the tranny. Without a tray I feel like throwing the tranmitter away after only a few minutes of holding it. For building I use a high end wrist brace especially for repetitive motions, like sanding. Painting with a brush is out of the question but I have no trouble with a airbrush or rattle can paint. Also, been building /assembling ARFs, instead of plans or scratch building.
Flexing or using your joints is helpful but don't overdo it. Finally, find a good rheumatoligist that can prescribe medications and recommend excerises to keep you moving and enjoying this great hobby. Good luck in all this.
Art ARRO.