IMO, they don't necessarily grow slow for the first 4"-5". After that they can be a little slower, especially if it's a female IME.
I'm not a fan of the single front, but I know lots of people do and/or have done it. The main concerns are picking good tankmates so that the front doesn't get stressed from too much activity, can compete for food, and doesn't eat his tankmates. Mbuna typically aren't good picks based on those concerns. Peacocks are slightly better. Haps are the best.
On the brightside, you at least have a larger tank to move him to if needed. That's better than a lot of people can say. Give it a shot if it makes you happy.
