It seems conceiveable to me that you could house those fish in a 55 gallon tank as long as you have a good water change schedule and filtration. Also, it might be good to have a divider to help stop aggression. If you have the money though itd be great to have a 75 gallon, thats what i started with and its great. The 75 gallon is very good for beginners because the large size helps prevent large swings in water quality, temperature, etc. It sounds like you have the desire to be a great fish keeper, keep up the good work. It's good that you sought more information than just what petsmart or whatever gave you, i started with petsmart and that was a mistake, all the info they give you is crap. I now go to my LFS and the staff there are very knowledgeable, if you have one of those in your area itd be better to go there.