+1 on the disc ready fork. Don’t skimp there. Santana’s may use a different diameter steering tube so your selection may be limited. I would also recommend speaking with a frame builder first regarding the chainstay. I previously explored converting our mid 90’s Santana Visa to couplers and disc and spoke to someone at Bilinky and he said he would have to inspect the chain stay to insure it was strong enough to be adapted to disc brakes.
i don’t know if this is an option, but does Magura still make hydraulic rim brakes?
Don’t give up, it is more fun to ride than to not.