Wow, it sounds like you have a tank just like mine! I have a 90 gallon tank, with a variety of fish. I bought my Lima about 6 months ago, when he was 5 inches long. He is now about 9 inches. His tankmates are... (1) 6 in. Iredescent Shark, (2) 6in. Pictus Catfish, (1)5 in. Jurapari, (1) 4in. Angelfish, (1) 7 in. Pleco, (2) 5 in. Bala Sharks, and (2)small Cory Catfish.
I find that the Lima minds it's own business. He swims around alot, but I never see him eat. He likes to come out at night, so don't the other cats. The problem that I am going to run into, as you might, is that your tank may get too small for the fish. I have accepted the fact that I may have to get rid of some fish so that the Lima can live. My suggestion is that you go with something that does not fit in the Lima's mouth... like a pleco or a Jurapari (Love them). Jurapari's are a type of cyclid. They are very active.
*celebratesmiley*