like any other fish you may collect as a hobby you keep them in a tank community or species only is up to you I see no problem in having them in a community tank as they normally get on well with fish of there sizes, if the other fish are small you may see nipping if so remove your angels to keep them alive and if the angels are bigger you may tend to see a bit of bullying if so watch with caution and decide yourself what your going to do about the situation. when keeping angels you must remember to have a heated tank and some sort of air flow like a air stone in the tank to help them grow and live for many years.
well most people ask this but its quite simple look at your local aquarium for them or find a specialist breeder and go and see there fish before you buy any just to check the conditions of there water and setup as they could be unreliable and have deformed fish growing and dying quite often which isn't good.
this can be due to many reasons such as the ph level of your tank, the fish that are in the tank with the angel , the algae that is growing quickly in your tank and even many diseases that have come into your tank without any notice that other fish might be able to stand and tolerate if so keep an eye on your fish and buy some medicine if need be.
Fry is a term used for baby fish and its exactly that with angels baby fish they are born from the angels eggs after breeding and they tend to grow nicly into angels if you take the right approach to them and care for them as well although they need some different attention and in the first few breeding lots not many if any survive its worth your while.
when your ready for the responsibility and your old enough to understand how fish work and what is required on the daily basis.