I am currently at two tanks. One is here with me at my dorm (10gal), while my 29gal is back home. I am still getting into establishing my first planted tank, and so far it is living up to my expectations, with a minor hiccup here and there.
My secret is a whole lot of reading before doing anything. This is a hobby where much time (and money!) can be saved if you know what you want to do and how you want to do it beforehand.
My ultimate goal is to one day have 5 ADA tanks. 2 Mini tanks, one 60P, one 60F, and a 90P or 120P. I think this is realistic, but it will take time, as with everything else. Hopefully over the summer my 10gal will be updated to a 60P. I want a miniM or L before I graduate college. After then, who knows.