First off reddit tends to be an absolute dumpster fire when it comes to advice as a lot of people have their heads up their butt and give wrong advice then when you correct them you get yelled at and banned, so stay away from there.
Most people on reddit believe those absurd max sizes of bichirs on google so that isn't surprising
+1. Reddit is not a good source. This is the best forum for your fish. Other good sources are fishbase.se and seriouslyfish. A good starting point is AqAdvisor. As for your Senegals, they should be good in your tank size. I would suggest a wider tank, but I understand financial problems and how frustrating it is. You can keep them in that tank long-term, but can also upgrade to a larger tank. Potential tanks include 55g acrylic, which is 15" wide and 18" tall (I have this tank), a standard 75g, which is 18" wide and 20" tall, and the tank I have currently, a 90g wide tank, which is 2'x4' and 18" tall. The larger and wider you go the more species you could put in. If you go to a 55g, perhaps you could try your hand at a Delhezi (which is a really active and rewarding fish). At 75g you can try some of the rarer species. Mokelembembe, Polli, Delhezi, and maybe palmas.
Pellets are staple for food, as Deadeye said. As a juvenile, my del loved Brine Shrimp. He is not a fan of Hikari Sinking Cichlid Gold I give him now, but still eats it. As they get older you can start to vary their diet with fish fillets or market shrimp.