I have had bichirs before, and they do take a bit of time to find the food, so with tinfoils they would surely starve.
The last two poly senegalus I had would eat from the surface. When I approached the tank they would rise with the other fish waiting for the pellets. They would just skim the surface grabbing at pellets once their mouths touched them. They do have a great sense of smell, but when I added silver dollars to the tank they could barely get enough food even when waiting for it at the surface. I had to hand feed them shrimp stuffed with pellets. And SD's feeding habits are like Tinfoils. I think you have already come to this conclusion though.
The RTGG get big. They use the word giant in their name for a reason. Space wise and with the bio-load I don't see the fish being very happy in the long term. I haven't kept RTGG, but I have seen them in tanks here and if they decide one day they don't have enough space, they will kill to make more space. Just from what I have seen and heard from people who have kept them.
Im not to familiar with Hoplerythrinus.