If you went with haps (many get large as adults 8+ inches) you could have a great mixed tank with lots of fish and lots of color. It would be a active tank as well. I have the following fish in my 135 gallon six foot long tank:
2 venustus (male and female)
2 red fin borleyi (male and female)
2 red empress (male and female)
1 malawi eye biter
1 brichardi (get more than one and they take over whole tank !!)
5 Peacocks (albino strawberries and Ob and stuartgranti)
1 peaceful mbuna (omnivore)
All of these fish are young adults now, breeding is occuring. No aggression issues for me. Half of these fish seem to love sifting sand. They are sand sifting haps. I would go with the regular sand , more options for if you change to new worlds later etc.. Easy to clean and maintain too. Just try to keep it around 2 inches deep (where the border stops on the edging that encircles and supports the bottom), deeper and you can get trapped gasses and ugly algae visiable through the glass. BTW fine black sand looks best with highly colored african cichlids. Look around online for Tahitian moon sand on clearence. I found some last month for 20 pound bag 8.99 plus shipping. Black background too.
I also have 6 fronts in there right now but do not plan on keeping fronts with the haps/peacocks permanantly. Only because fronts are very shy and not aggressive feeders ( i have trouble making sure they get enough food.)
IMO Fronts should be kept as a colony only and not a single fish in a big hap/peacock tank.
If you wanted the brightly colored 30 fish senario I would instead go for a peacock tank, peacocks tend to stay smaller and you might be able to do overstocking with over filtering and make it work. Mbuna are the other option for 30 fish in a 135.
If you go with Mbuna do your research on each fish you plan on keeping. Any of the Metriclima species are particularly aggressive ! Other mbuna to be careful are Kenyi and bumble bee. Avoid any that are listed as highly or hyper aggressive. Trust me on that , i found out the hard way. All is good when they are juvies but the instant they reach maturity they start killing tankmates (2 or 3 fish a night)and that is expensive and disappointing. Mbuna love tons of rocks stacked like a rock pile and are cave dwelling. I did notice that my eye biters and brichardi along with the most aggressive peacocks do ok with the mbuna i have (after i removed the killers LOL). I feed all of them the lowest protien lowest fat content sinking cichlid pellets i could find and have had no problems so far (about a year like that)
If you were just looking for number of fish you could also do a species only brichardi tank. Buy 5 , when 2 pair off get rid of the left over (return or sell them) and that pair bonded couple will breed like crazy (in one to two months i went from 3 brichardi to well over 100 brichardi because of their breeding. They also live as a family group and both care for the fry and fry live with parents (adult males will eventually be "encouraged" to leave the group LOL)
That would be a spectacular tank and the fish are one of the more beautiful types with those fin extentions in my opinion. You could then sell fry too.
2 venustus (male and female)
2 red fin borleyi (male and female)
2 red empress (male and female)
1 malawi eye biter
1 brichardi (get more than one and they take over whole tank !!)
5 Peacocks (albino strawberries and Ob and stuartgranti)
1 peaceful mbuna (omnivore)
All of these fish are young adults now, breeding is occuring. No aggression issues for me. Half of these fish seem to love sifting sand. They are sand sifting haps. I would go with the regular sand , more options for if you change to new worlds later etc.. Easy to clean and maintain too. Just try to keep it around 2 inches deep (where the border stops on the edging that encircles and supports the bottom), deeper and you can get trapped gasses and ugly algae visiable through the glass. BTW fine black sand looks best with highly colored african cichlids. Look around online for Tahitian moon sand on clearence. I found some last month for 20 pound bag 8.99 plus shipping. Black background too.
I also have 6 fronts in there right now but do not plan on keeping fronts with the haps/peacocks permanantly. Only because fronts are very shy and not aggressive feeders ( i have trouble making sure they get enough food.)
IMO Fronts should be kept as a colony only and not a single fish in a big hap/peacock tank.
If you wanted the brightly colored 30 fish senario I would instead go for a peacock tank, peacocks tend to stay smaller and you might be able to do overstocking with over filtering and make it work. Mbuna are the other option for 30 fish in a 135.
If you go with Mbuna do your research on each fish you plan on keeping. Any of the Metriclima species are particularly aggressive ! Other mbuna to be careful are Kenyi and bumble bee. Avoid any that are listed as highly or hyper aggressive. Trust me on that , i found out the hard way. All is good when they are juvies but the instant they reach maturity they start killing tankmates (2 or 3 fish a night)and that is expensive and disappointing. Mbuna love tons of rocks stacked like a rock pile and are cave dwelling. I did notice that my eye biters and brichardi along with the most aggressive peacocks do ok with the mbuna i have (after i removed the killers LOL). I feed all of them the lowest protien lowest fat content sinking cichlid pellets i could find and have had no problems so far (about a year like that)
If you were just looking for number of fish you could also do a species only brichardi tank. Buy 5 , when 2 pair off get rid of the left over (return or sell them) and that pair bonded couple will breed like crazy (in one to two months i went from 3 brichardi to well over 100 brichardi because of their breeding. They also live as a family group and both care for the fry and fry live with parents (adult males will eventually be "encouraged" to leave the group LOL)
That would be a spectacular tank and the fish are one of the more beautiful types with those fin extentions in my opinion. You could then sell fry too.
im pretty set on peacocks and haps because they are so colorful and i want people jaws to drop when they walk right in the front door. i MIGHT try to add one brichardi but most likely not. 
just will have to keep dreaming about one for another couple years. no one has said anything about the thick skin from victoria, too aggresive still?