Bodacious Cowboy

Just rough arch and take the edges down to desired thickness plus about 1mm, then use your slotting saw to cut final thickness. Then gouge round the plate above the saw cut until thin enough to snap off, revealing your flat platform. No need for all that tedious drilling.

Don't know, never used one.

This is a natural consequence of using a non-full-thickness mold, unless you are very careful with bending, fitting and gluing of ribs. With a bit of practice you can learn to "tune" your technique to achieve the degree of wonkiness you desire. A certain degree of asymmetry can make things look more interesting. For perfect perpendicularity you need to get the ribs fitting very well to the form (I can see some quite large gaps in your photo), and glued up so that the rib is straight (ie rib edge parallel to the end block and equal "overlap" with each corner block....). I don't think it's anything to do with your flattening process.

I concur with Conor's sentiments. Not really fair to condemn the luthier without knowing the full context of the conversation. Some players expect soundpost adjustments to function like some kind of graphic equaliser.

Totally agree (also likely to have a cleated back joint as part of the deception).

Are you using toothed blades? I'm not being snarky by the way. I just think part of your problem is likely that you're doing too much wood removal with the scrapers. Scrapers should be just for removing plane marks, ideally.

No, it’s the bumps that need to be planed out before scraping.

That doesn't look ready to scrape. Some planing needed to get rid of those bumps.

I'd say most people who buy antiqued instruments do so simply because they think they look nicer/more interesting than fully varnished ones.

What a bizarre thing to do.

https://www.andrewcarruthers.com/simple-carving-jig/ From Andrew Carruthers web site. In case my description wasn't clear enough.

Clamping the plate ends between 2 cork or leather faced blocks clamped to the bench.

No disrespect to the very fine makers on this forum and elsewhere who use one, but you really don't need a cradle at all if your center joint is good enough.

yes indeedy