I wouldn't do one severum I had one in my 125 an it got very large an a bully. I would also go with a pack of smaller loaches like yoyo's. They will be much more active an entertaining then a pleco an Raphael.
I already have the sailfin pleco and Raphael catfish in my 30 gallon and will move them to my 75 when it's set. But there is no way I can part with my raphael catfish, he is very active for his species plus I am a catfish lover.
Tapajos should be fine. Not sure about firemouths, if you have a small group they may ignore the angels . Heckelli are notriously hard on each other especially in smaller tanks, they're late bloomers but its common for them to start eliminating one another after a couple of years when they hit maturity.
On second thought, if I were to skip the angelfish would a red shoulder severum, firemouth, geophagus tapajos, and one other medium cichlid along with the previously mentioned bottom-feeders work?