My series 3 was in about the same condition (but MOT'd...) i wanted to just run it as is but the front suspension was seized, the gear selecter dodgy, the tank and tap rusted tf and the cables and loom on their very last legs and some crankcase studs held in with muck alone, a fin missing on the flywheel too. The exhaust weighed a ton and needs replacing. It'd run but if it broke it'd take a while to fix. The more I look the more needs looking at, even though they are pretty much bullet-proof enginereed.
I'm going for the frame + forks + hubs and under-panel stuff powder coated, respray the loop, replace all nuts and bolts, engine overhaul (a new gear selecter arm is a bit of a mare), powder coat and recover saddles and leave the panels as they are, ACf-50 and maybe some undercoat on the bottoms. It's still a full strip and rebuild to keep it rusty

Rustoration isn't easy but it'd look sweet. hope it turns out OK.