Honestly? Start small. Force yourself to get bigger. Right now from your experience working at Circuit City, you probably have a pretty good customer base. If you tell them you do installs on the side and carry a few lines of product, they'll start coming to you for future installs.
You obviously need to carry brands that the public knows and calls for (Pioneer, sony, kenwood, rockford, MTX). But it would be good to throw in a few good ones as well (Eclipse, USamps, cdt). Keep all of your inventory floating (don't pre purchase in bulk) Maybe buy a few showroom pieces until you have the capital to support having more around.
Get a wholesalers license and create a LLC (Limited Liability Corp). Find a local wholesaler that you can get cabling and other install accesories from or obtain a dealers license to carry those types of products. That stuff you're going to want to have on hand (bulk wire, RCA's, fuse holders, fuses etc).
Really the hardest part will be setting up the business legally. You need to be state approved with a Tax ID and all that fun stuff. Other than that, stay simple with what you know.. and that way if things happen to not work out.. you really don't lose any money. If things start to get better.. carry more product on hand and find a building.
That's all I got for now.