50 gallons is a good size aquarium for Cichlids - so a good start.
1. African Cichlids such as Yellow Labs require Hard Water - to achieve this use rock and marine type sand - these will help the water hardness and buffering capacity which is important in African setups the PH level should be a constant 7.5 or above eg. 8.2
You will require test kits for GH, KH (General & Carbonate Hardness) such as Nutrafin GH\KH kit by Hagen as well as PH.
2. Five Electric yellows would be good, Electric Yellows from what I read and seen are one of the most peaceful Cichlid. Try if fish can be sexed to get 1 male to 3 females.
3. If only keeping Yellow labs you do not have to rearrange the rocks, although you can do so. This would only sometimes be required when keeping more aggressive fish.
Do you only want Electric Yellows? if you would like a varied set up I recommend the Cookie Cutter at
http://cichlidforum.com/articles/qui...rence_list.php
Good Luck - Electric Yellows are also on my list for my new tank. They sure are colorful.