I would think you would be better off acting as a dealer for existing amp builders and perhaps they would consign amps to you for display/tryout. To build amps, you'd have to stockpile parts, devote some amount of space, have a reasonably skilled person and theoretically a test bench and build bench with gear---which need not be very expensive and can be used for other things, but still. For you to build amps you'd also have to market/advertise the things, as well. It also might change your classification for worker's comp (from sales to mfg) which is very punitive in CA. Over and above that, philosophically, it's quite a different business than running a store. Of course, if you could morph into an amp repair biz, perhaps that could be a positive...but the two are two rather different businesses.
When it comes to the current level of boutique amps....I think most people underestimate the amount of time it takes to produce a really nice looking build and that is probably what you are imagining. The cabinetry is a PITA, but I suppose you could outsource that.
You're in an affluent area (I used to live in Playa del Rey) and people have money and you're not trying to be a Guitar Center. I don't know how big your store is, but rent is probably not cheap where you are, so the overhead of the req'd space is not going to be cheap.
My attitude about operating a retail store is kind of negative, I acknowledge. Been there, done that, would never do it again. There is a giant fundamental difference between reselling things that are supplied to you pretty much or exactly how you intend to offer them, and crafting something all the way from punched metal and tube sockets and lockwashers and 6-32 screws and amp corners and handles and writing and producing the documentation/manual all the way to a finished product.