[quote]So, at some point I do intend on owning a firearm, but being the type who likes to heavily personalize stuff if given the option...[/quote]
You should look into Glocks. They're budget friendly, easily customizable, incredibly ubiquitous and user friendly (both on use and most customization).
California's requirements for self-made/assembled firearms makes their construction inconvenient.
You'd be jumping through hoops unnecessarily and (probably) wind up having a firearm of lesser quality as a reward for your time & trouble.
They do, on sales at least. I know of more than a few folks that drove to Arizona, Oregon or Nevada to buy high cap mags before they left for more firearm friendly climes.
In any case, I'm not sure if their possession is banned as well, or if it's just their sale.