I have been a long time keeper of fish, but due to massive moves have been reduced to 0 tanks, my gracious wife has given me a 150g limit in our new 2nd floor home (our home is over our garage) The previous owner built the home and due to weight we both decided 150 was fine. Now I would like opinions on the tank, I was looking at 1-150g tank or 2-75g tanks. Previously I had 2 55g and a 29g, all were set with UGF with powerheads and about 1.5 inches of gravel, and an size proportioned canister with biowheel. On my old tanks, my water was CRYSTAL and the water tests showed VERY low nitrite and ammonia (unless a fish died and I missed it). I admit, I did NOT do water changes very often, due to the fact the water tests were showing as very healthy. I do overfeed lol. Now I was looking at housing 2 Pacu, 2 Jack Dempseys and some channel catfish. Previously I had convicts, peacocks, clown knives, some crabs, mussels, clams and 3 VERY agro crawdads... The Pacu ended up in my pool due to size (have a 7200g 18ft pool) and someone "donated" 2 arrowanas were found in the pool one afternoon to my surprize... When we moved the pacu and arrowana were gladly kept by the new owner of the home lol. The rest went to the LFS. Now I am looking at a whole new setup and cost is a minor factor I was going to go with what I know, but at this time there is alot more options then there were when I started in the mid 80's... Now we have more then just gravel, my local LFS is TERRIBLE the tanks are all nasty and the place reeks... So I avoid them. I do have a reliable shipper for the fish I want, now I need help on 2 75g, or the 1-150g and the setup. I was looking at the clam/mussel/snail combo again, but I read they can house many things I do not want. There are so many topics about everything here and so many opinions that it is hard to sort FACT from Opinion... 
wish you luck with the tank filtration buddy!