Ditto--I've heard that showcases are pretty much a waste of money .
One thing I DO recommend is joining the MDC etsy street team (PM me for details!) we are planning on going in together to buy some advertizing here on MDC this fall probably, possibly also a print ad in the actual magazine. We also have a team blog with everyone's links on it and it gets quite a lot of traffic--all the team members here who have advertizing siggies put the link in their sig, so even people like me who can't affort the ad sig can still benefit because i'm on the blog. I just try to send people there other ways since I can't do it this way.

As for usernames, Savannah smiles is correct, your username will be your shop address, so I STRONGLY recommend making it your shop name, or at least some variation on it. My original username was davejenni1203 and after two years I just recently deleted it. i'd been switching things over to a different shop for some time, and finally had built up some feedback on the new shop so I deleted the old one. If you have a funky (not easy to remember) username, or your username is different from your shop name, and ESPECIALLY if you don't have a ton of feedback yet, i think it's worth the trouble to start over. If people can remember your shop name/address that's a really good thing for sales!!!