Renaissance plexiglass guitar from 1979.

I would try to start small and spend as little money as possible, because it may not ever play that well no matter what you do. I have a handful of old Japanese guitars and I've got to say, the hollow bodies are mostly good for wall hangers, its always going to be prone to feedback etc, the sold bodies OTOH can be pretty decent. It might also benefit from a fret level and/or neck adjustment. Just get some new slider switches to replace the bad one(s), IMO it ruins the vibe of the guitar to replace those with a toggle switch.

It looks like it already has an adjustable bridge, so thats good. Tuners are probably going to help a lot and will probably be your best bang for buck improvement (as long as you don't buy really expensive ones). Keep in mind that you may be limited to true surface mount types if you don't want to cut into the body (though you may have more wiggle room since its a hollow body). For pickups, you might check out GFS, they have 'gold foils' and some true surface mount pickups too. I'd do a non trem tailpiece as you can do that a lot cheaper than a bigsby.

Decca teisco guitar