Hi Balloons&Killies
As DiscusKeeper has said, you should only really be keeping a mated pair in that size of a tank. This is because Discus can be aggressive during feeding times and just during everyday stuff.
I have a 50gal and have seen this firsthand with my discus, i purchased 2 red turqs and placed them in the tank with 4 albino cats and 2 BN's and one is always pecking, charging and generally annoying the other. It isn't so bad and the other fish gets his fair share of food and space etc but with a couple of more moodier discus it could present a problem as some discus become territorial during feeding and can stop the other discus from feeding, eventually becoming stressed, sick.. and eventually die.
All of the above is not a problem with a mated pair as they wont hurt each other and will most likely breed for your if you can get everything right.
I am aiming for 4 discus as a mimum in my 50 gallon tank with #4 coming this week in the form of a blue turq to add to my 2 red turqs and red dragon.
As far as strains go i wouldnt have a clue, there are so many colours and strains etc.
Good luck and if you need any additional info dont hesitate to post, all the discus keepers here so far have been more than approachable regarding advice =-)