Any kind of angel would be fine, but I think you are limited to two once they are full grown. What a lot of people do is get 4-6 little ones and eventually at least two will pair off. Most better LFS will take the others back. Due to their cichlid nature (somewhat aggressive during spawning)and tall finnage, two is max for that size tank, plus a few other fish like cory cats, a pleco or otos, etc. I suppose the ideal pH would be 7, but as long as the pH of the LFS where they came from (or the breeder's pH) is close to what you have naturally in your water they should do fine. My pH runs high at 7.6 or so, and because I got my angels from a LFS on the same municipal water supply they were already acclimated to my water. I think this holds true for many fish with a natural wild pH that may be different than what they are bred in, so they are adaptable and you needn't be timid about getting fish that are supposed to require a particular pH. It is much easier to get fish that are adapted to what you have already than trying to maintain a drastically different pH in your tanks than what comes out of the tap.