Number one 50 gallon is a great starter tank, if things go wrong it gives you some time to fix it.
and check out the forums and all the stuff on www.fishindex.com
they are great and willing to help a newbie.
But first you have to decide what you are going to raise.
I have 3 tanks
a 20 gallon african cichlid tank, a 33 gallon freshwater and a 2 gallon goldfish and I love them all but problem is money goes into them and not my car LOL!
Study what type you want and then what fish, with a 50 gallon you have a ton of options. And the it doesn't have the be a deep tank a wide tank is better(but hard to come by)
Anyhoo good luck and tell me what you decide on I am really interested.