Bichir | Any Other Starter Fish
Umpteen 0
Go bichir! Get some!
Anyways...
If you have a 75g in storage, then your options are grand.
I have a green terror with a bichir, they grow about the same rate so it's worked perfect for me so far.
Most medium-large cichlids will work as a "tank boss" while the bichirs will lay around like a bunch of iguanas on the bottom, and you should get some top fish too.
Nothing really strikes my memory of medium sized top swimmer predator so you'll have to ask around.
If your planning on upgrading the 75 then you could get a arowana for a while!
You'll have great fun with the bichirs, you should get like 3 or 4 of them at least so they'll be more active.
Geophagus or any of the other earth eaters would probably be perfect for you. Schooling, active medium sized cichlid
Good luck!