That mostly makes sense to me. Adding mineral spirits will reduce popping (air entrapment) and will cut down on the sanding.

Maybe I'm just a masoshist for sanding, but I would never get away with using 150 grit on a varnish. I would end up taking too much finish away. 400 grit is a lot safer, and the water helps lubricate and cool the phenolic. It takes a while for them to develop full properties, especially the mechanical properties.

Wrinkling can be from too thick of a film, but there are two other common causes: putting on the next coat too soon or having too much air circulation while the coating is drying.

If you place the next coat on before the previous is dry enough, the solvent from the freshly applied varnish can actually attack the previous coat.

If there is too much air circulation, you can have the top layer of this coat drying so much faster than the bottom that the dried part sinks into the still wet part. This creates a wrinkled surface. The same basic mechanism as too thick of a coating, though with a different cause.

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2010 Toyota matrix

'93 500 SEL
Well, I sold it. Just got to be too much to keep up with.
First time I haven't owned a MB since 1983.

'12 Volvo S80 T6
Needed something that wasn't as hard to deal with as my bad addiction

'18 Mazda Miata
No more boring cars for everyday transport!