Get as many as you can afford. Yes, they are aggressive though stocking density can control that. Get as many females as you can. You do not want to only have 2 or three males though. I would rather have 5 or 6 males than 2 because you will quickly have 1. At least with a few the aggression is dispursed from the alpha fish.
Hi. I hade msome of them in the past. The male was so about 35 cm long, very nasty. Has was agry to all my fishes he could get. Later he goers on a journey to a friend and there he killed one of his longola males very soon. In my opinion it wil be a disaster with only 10 of them, only with some Tropheus!! But it is your decision. But remember, who of this, who said " it will works", has already hold some big Petrochromis!!!! I had also some Macrognathus rainbow with 35 cmand some kasumbe orange with30 cm. Together with the Ubwari they are the biggest killer i have ever seen!!! Now i have some red, together with some longola and some moshies. It works in a 370 gallon tank and with 35 fishes.
But it is your decision, i can only say they are terrible petrochromis!!!!!!!!!!!!!!!!
My experience with this fish has been that the ubwari is one NASTY mofo. I have kept and keep several types of petros(moshi, ikola, texas gold, longola,trews,tricolors and ubwari, famula nyanza) and the ubwaris, at least the ones I had were impossible to house together. Just brutal. I had 10, forget the ratio, but several males, and they were housed with moshi and ikola and they couldn't be kept in the same tank - 6 footers 150, 220. I had them in hospital tanks most of the time. That was my group and I know they aren't all the same but pretty much everyone elses experience is the same - they are difficult. I have one 7" male left (sold the others) in with 10 6-8" moshi, a large texas gold male and a smaller female. He runs at everybody and rules the tank. Nice looking fish but not nice enough for me to try again - just plain mean. like my simo diagrammas - nasty, nasty mean. But that's the world of petros - expect a lot of babysitting amd losses despite your very best efforts - they are all unpredictable and capable of serious damage in very little time.
I live 40 miles away from Peter Ruben (Atlantis New york, USA) New. He had some for sale... I am glad that I did not purchase them.... I don't need more problems.... The WC Moshi and the WC Longolas and the TR Famula Kasiers were real nice.... no problems....