Well I'll say that my story is rare so wait for other people to give you a better idea.
When I got my ray I had a 60 gallon tank and about 3 mounths of aquarium hobby under my belt. I started out with a retic, saposidly one of the harder rays. I was doing water changes once a mounth and feeding a blood worm cube a day. Lets just say then i found mfk and people like miles and nic save me. Now i have a 150 gallon stingray pond and doing water changes a whole lot more than once a mounth (still should be doiing more but...). I wouls suggest to start with a motoro the are said to be the hardiest. Imo a 5'X6' pound will be fine for around 3 motoros. Some people will tell you "oh no thats not big enough for life motoros get 36in" but there are very few motoros over 24", Agian just my opinion and people will probabley have diffrent to say. Hope this helps.