Definitely want to suggest the Metropolous build guides for Marshall clones on the Valvestorm storm website as a great guide for assembling power sections and wiring, in addition to a good build guide for a Plexi.
Also would point toward the Hoffman forum as the best amp tech support forum I found in building 7 amps so far. The TDPRI forum is great as well.
One more thing I'd suggest for anyone building amps that use 6V6GTs is that NOS or ANOS 6V6s are dirt cheap and are a better buy overall. I've bought a bunch from this seller:
https://www.etsy.com/shop/Lowtechelec and have been very satisfied.
I started building pedals back in 2015 and it took me a solid 3 years before I felt comfortable enough to start on amps. Every amp I've built has worked right off the bat, though I did have to rebuild my 5E3 because it was too clean. That amp in general ended up being the most challenging build because I have large hands and the chassis is tiny.
I've been only building pedals for the last year or so because I haven't found any other amps I am dying to build. I do prefer amp building personally though. Something about it is more satisfying than pedals.