The location of your premises is going to be one of the biggest considerations for you. Obviously for a mail-order or internet site, location is pretty much irrelevant, although somewhere in easy reach of a good post office and not too out of the way is best.
If you're setting up shop then the high street is going to be your prime spot. The downside is that it's expensive, and to compete with the big chains you'll need to spend a fortune on shop fittings.
says, "Each record shop we open now is typically 3000 sq ft - and with shop fitting at around £100 per sq ft you can spend anything between £500,000 and £750,000. But opening in the back street all you'll need is a few boxes."
Another aspect is how you should display your stock. It's displayed either dead (just the empty cases) or live (the whole package). Obviously if it's dead then you're going to need a second set of shelves behind the counter to house the CDs; if it's live then you'll have to invest in a fairly expensive security system.
The main advantages to a live system is that you can have multiple checkouts around the store.