Senegal, delhezi, retropinnis, mokelembembe, palmas palmas, palmas buettikoferi, palmas polli would all do good in a 75g. Teugelsi, weeksii, and ornate will eventually outgrow your tank. However with a weeksii you may be able to house it for a while as they tend to grow slow. Depending on how much decor, filtration, and tankmates (as well as WC routine, feeding, etc..,) will determine how many you can put in there. 5-6 would probably be a good number, but if you really wanted to 7-8 could be doable. Anything over that may be pushing it.