Well yeah, I mean you gotta build it up. But either way can work, its really up to you. If you want a brand name then you can still develop fine, it just may be easier for search engines with a descriptive name.
Huh? Are you saying that to get a 4 letter domain, just reg. ABCD143.com? If so, dude, you should stay out of the domain business.
google "web 2.0 name generator". I can't remember the URL, but there are a lot of clones now. It helps a lot