Hmmmm...in truth, 3U x 84 hp isn't a good way to start. It'll force you into one of two situations...
1) You wind up using very slim modules, 6 hp and down. This has an inherent flaw in that if you don't have fingers about the diameter of spaghetti, it'll be a total bitch to use.
2) You put normal sized modules in, and then run out of room before one or two critical modules can be installed.
I don't endorse either possibility. Instead...and you hear this a lot here...get a Tiptop Mantis. US street on it is $335, and you can add a second Mantis later on with their expansion bracket set. Power supply is also quite hefty in those, and unless you stick several tube-based modules into the build, you're not likely to exceed the current capacity, even on startup inrushes. They're lightweight, and Tiptop even makes an optional gig bag for them.
And speaking of Tiptop, they're working with Buchla on a line of 200-series Eurorack modules. The 281t and 258t are supposed to be out around the end of the year, with the 245t, 257t, 266t, and 292t dropping during 2022. And with THESE, the Buchla "price tag" is gone; the 281t is $210 and the 258t is $200. Given that there's other Buchla or Serge-based Eurorack modules around, you could easily build a pure "West Coast" rig in a single Mantis. But don't try it in the cab you've got above...you won't have room.