Ehhhhhhhhhh...you can go plant pretty easily and with success. I don't know why people keep to an old, and in my Opinion unfounded/misguided, dogma that Africans are a no no with plants. It can be done, no question.
Crinium (Onion Plant)
Vallis (and giant)
Java Fern
Java Moss
Anubias
Amazon Sword
I've either planted these myself in my rift lake tank, or seen them thrive in others. There are others that have been suggested to me but I've not tried/seen them.
You need to ID the big guy before we can say whether he is a natural predator of smaller cichlids, but as a rule of thumb if Fish A can fit Fish B into its mouth, Fish B is likely to get a tour of the interior of Fish A sooner rather than later.
You'll get around that though by stocking fish of around 2 inches or more, which is the size most Africans are sold at, and stocking plenty in one go, like in groups of 5 - 10.
I wouldn't worry about having to move them sue to size - 75 is a fine size for most rift lake populations.
What's available locally to you ? Have you looked at Peacocks, Mbuna, Haplochromides and worked out which you prefer ? Do you have both male and female fish available ? These are the next things to decide.
