I would not get convict cichlids, they are aggressive towards other fish in the tank and even to each other! They are not great begginer fish, I had a pair of white convicts in a community and they attacked my other fish in the tank until these were stressed out, its the first spawn that triggers the aggression towards other fish as well as each other. They grow to around 15cm in lenght and I'd say the minimum tank size for the would be 40-50 gallon tank as long as possible as they will want to chase each other around the tank. While I had mine separated from other fish, the male convict bit scales of his gf's side and ripped her fins. Not recommended for begginers. If you want a specific kind of fish you willl need to know:Also Convict Cichlids from what I read are great beginner fish but I'm currently getting mixed opinions about tank sizes.Some sites say 20 gallons minimum For a pair while other say a minimum for 1 is 30 gallons.
-the nitrogen cycle
-water parameters, ammonia, nitrite and nitrate
-GH, KH and pH (crucial)
Can you provide these?