Sounds like it will look great, the Proton with blacker cladding is awesome!
Don't recall anyone else cutting it with mineral spirits when applying it with a brush.....
Is there an advantage to thinning it out with brush use? Maybe less streaks or something??
Thinning 15-25% with mineral spirits is standard for varnish especially the first coat. It brushes and flows much easier. I found this to be the case with SN, and got very little streaking if any. It just felt right.
Dave