Having more than one vessel is a great idea. That way you can get your pipeline full.
I spent some cash and got some extra 6.5 and 5 gals for myself.
There are plenty of discussions on the boards if you search.
I personally use glass - and I am find with that.
There are people that swear by the better bottles
and the plastic buckets work just fine as well....
I have been thinking of getting a combination to see what I like and do not like.
I personally think it is a preference thing.
Check out the wikki too. http://www.homebrewtalk.com/wiki/index.php/Carboy