First off, congrats on the new tank!
Electric yellows, or Yellow labs, are great little cichlids. They are pretty mild tempered compared to most Mbuna and are very pretty fish! I did my 55g with 5 Labs and 15 Demasoni. Make sure to get a larger number of fish when they are young than you plan on keeping for the long run. You're going to have deaths, re-homes, etc.
With my tank...about 4 months in the Demasoni's started killing each other off. Probably due to the fact that it was hard to sex them and get the appropriate sexing (1m/4f).
Since then, I have been adding many other different cichlids. I've had much more luck with a mostly-male assorted African tank. By assorted, I mean different types / looks of 'similiar' cichlids. This is a win-win for me because I love the different fish that I have.
Rough list: (being upgraded to 90g this summer before they are full grown)
1 albino zebra
1 blue cobalt
1 gt severum
1 bn pleco
They are all middle aged (2.5 - 5") and don't really have any major problems. My male Kenyii is nearly an inch bigger than every other fish. He patrols the tank and breaks up any sort of fights and literally just goes back to his business. You will always have some aggression, because you're picking an aggressive fish species to have, but most of the time the fish just decide to relax (in my experience, with MY fish).
Anyway... you're going to get a lot of information. A lot of do's and don't from people. You'll have to remember that it's your fish tank and you can decide what you'd like to try and what not to try. As long as you watch your tank and aren't hesitant to make changes due to the fish, you typically can stock as you please. (QT tanks are a must-have in my opinion) There's definitely some major rules to follow in fish-keeping, but with cichlids there's so many different types and so many different attitudes. Sometimes you'll get a mellow fish, sometimes you won't. Recently I put a Armored Bichir in with my EB Jack Dempsey after losing my Senegal Bichir I had in with her. My EB would not leave the new Bichir alone, she hated it. I took the Armored back to my LFS
and exchanged for a very similar Senegal to the one that I had lost. The EB now just leaves the Senegal alone completely. Fish have personalities and attitudes, it's strange to see what some fish will accept and others will not. You'd think 'oh it's just another bichir, they look almost the same except for the armored is darker!' but no, she could tell he was new and different and hated him, but accepted the Senegal.
With my tank, I have lace rock in the center. Not many caves, just kinda layed out around the center. The fish don't really have major caves to protect and hold for their own. Most of the aggression I've seen is over territory, but it's hard to build a territory for them without major caves / structures to take over. By overstocking a cichlid tank you can majorly reduce the aggression / losses in the tank. Just remember to get very good filtration if you do this method.
Good luck reading this wall of text,
. Keep us updated on your tank!