The nut slots don't make any difference to neck relief, that will remain the same even if you take the nut off completely. The nut slots alter the action height, just like the saddles do. I don't measure anything, but I've been doing this stuff for over 50 years now.
I gave up loud in the 1980s. If we couldn't hear our bandmates talk on stage then we were too loud. It wasn't usually the drummer, but the lead guitarists (yes, we had several that got their marching orders).
I'd try scraping the neck very gently with the grain to remove the finish rather than sanding. The Halfords alloy wheel lacquer has been recommended a few times. It's not supposed to yellow, unlike their standard gloss which turns an incredibly bright shade of yellow (not at all attractive on a...
It's not a vintage style ST62.
Its an ST362 Japanese Standard, from 1986-7. The modern tuners and serial number on the headstock are the main indicators. Prices pre-lurgy stupidity were about €500, what people are charging now is ridiculous.