I started with the Classique/First size, too, and worked my way up to larger bags. If you can, go see the bags IRL, at least to get an idea of size and shape, then choose the color. You can look though the "Documenting Balenciaga Colors" thread in the top section on this page to see a lot of options.
If you're going to go for an older color, you may have to wait a bit and deal with eBay. If you get a current season color, you have the great experience of buying a new bag, which is always fun. Someone posted a thread of the A/W (or F/W) colors, which will actually start coming out in the summer, so you should look at those and if there's something you like you can put yourself on a list at the store nearest you.
If you're going to go for an older color, you may have to wait a bit and deal with eBay. If you get a current season color, you have the great experience of buying a new bag, which is always fun. Someone posted a thread of the A/W (or F/W) colors, which will actually start coming out in the summer, so you should look at those and if there's something you like you can put yourself on a list at the store nearest you.