yeah that phoenix in your av would be awesome on your back... i'm a big fan of symmetrical tattoos... i like that one takumi posted up, that's pretty cool. also, try and be original, maybe modify someone else's design, but don't copy the whole thing... after all, you don't want to be wandering around for the rest of your life with the exact same tattoo as some stranger...
i'd echo what others have said about don't get stuff done in hard to hide places like hands, face, neck etc. Anywhere that's hideable is fair game...
One thing i have heard said is that people often go too small for their first tattoo, so if it's something you really like, go big...epic style
of course, that comes with a price tag, but meh... if it means a lot to you, price won't really matter.
shop around, go to a good shop that looks clean, and check out the portfolios before you get it done (all good artists should have one, should give you an idea if they're any good or not). all pretty common sense stuff, but i keep reading about people who get tattooed by a mate in their basement... it never turns out well
ok, i'll stop preaching and get off my soapbox...
btw, naval_fluff, your idea sounds pretty cool