Hi, kickngas! Absolutely listen to the Wife on that one!
I'd love to answer your questions! Glad I could be a positive influence on you to order the best price/performance speaker in loudspeaker history!
1) I used Zinsser B-I-N Shellac for primer: https://www.homedepot.com/p/Zinsser-1-gal-B-I-N-Shellac-Based-White-Interior-Primer-and-Sealer-00901/100398381
I used Rust-Oleum Sierra Performance Beyond Acrylic Enamel, Black, Satin: https://www.rustoleum.com/product-catalog/industrial-brands/sierra-performance/acrylic-enamel-coatings/beyond-acrylic-enamel/
2) I assume you mean the quality of the before mentioned materials. I'm quite impressed with both. The Shellac lays on THICK, which means you can really sand into it. You can lay it on thick enough on the edges, wave guide, and all the exposed MDF edges that you really don't need to fill them. If you want an absolutely perfect finish, you still may want to fill the edges. One thing I've always heard shop guys do (which I haven't tried) is mixing sawdust (MDF) with wood glue to make a really good fill. It's basically the same composition of the MDF itself - Just more glue.
3) So, this was a bit of a trial and error mess. I started with an HPLV gravity sprayer, since I have a nice compressor that can easily power one. This was my first time using one. The nozzle I got was too small, so basically the paint dried mid air when I was spraying. Which led to a pebbly surface. This needed to be sanded down between each coat. Finally I said screw it, and was about to order another nozzle, then my Dad said he's been wanting to get a Wagner spray gun to paint the house with in the future anyways. So we decided to try that out before putting more time in the HPLV. It worked great... They have a smaller nozzle for detail work. Much easier to use... https://www.wagnerspraytech.com/products/paint-sprayers/flexio-590-paint-sprayer/
4) I believe I started with sanding the raw cabinets with 200 grit (after glue up), sprayed a coat of primer. Dry. Sand with 200. Blow the thing with air, then tack cloth right before spraying to clean it. Coat of primer. Dry. Sand with 200, then I think 320 or 400 we used. Blow with air, then tack cloth. Spray a coat of finish. Dry. Sand with 400 I believe. Blow with air, then tack cloth. Spray a coat of finish. And that was it. I haven't wet sanded them yet... And I'm not sure if I'm going to. They look pretty good as is.
5) Obviously I would have started with the Wagner gun. Also - I would have prepped the glue joints a little better with more filler. Some of the joints can show thru, but it's hardly noticeable. The MAIN thing I would have made sure to do, was the last finish coat I would have put on thicker. It's hard to tell right when you're painting, because it looks totally uniform and finished. But after it drys, you can see some spots that there is a little less paint, AKA the texture is slightly different... It's a balance of enough paint to not get the pebble finish, and too much that you don't get orange peel or even worse, drips. As far as the crossover, wiring, that side of it, I wouldn't have done anything different. Maybe in the tweeter circuit upgraded to Path resistors, copper foil inductors, and replaced the Erse cap with something else. BUT, I'm planning on doing this in maybe a year or so, and the way the crossover is designed, it can basically just be cut out, and the new section transplanted right in!
Hope that helps! Feel free to ask any and all questions you may have! Congrats again at starting your journey to some of the best speakers available today!