If you're going to end up with a 150, is this a standard or wide tank (wide is 5x2x2x)? A 2-foot catfish like a tigrinus shovelnose would really be too big for a standard 150 as its length is greater than the width of the tank. I'd look for something ranging in size from the jaguar catfish to the lima shovelnose that you're considering. I think a lima is a very good idea and you could put some of the milder species of cichlids with it like a severum, uaru, geophagus, etc. I'd avoid any breeding pair of cichilds in that tank though as they will take over most of a 150 gallon.