For the fish that I am going to get:

angels
cories
rosy barbs

What type of heater and wattage, filter, plants ext should I get. I am planning on some live plants and I hope the fish won't be to rough on them. I am not sure exactly what temp the tank should be, the tank is a 55 gallon. Any suggestions would be helpful.

78 is a good temperature for most tropicals. Just remember that angel fish get very big and will eat other fish big enough to fit in their mouths. As for heaters, u could get 2 100 watt heaters and place one on each side, thats what I would do anyway

I would suggest a 200-250 watt heater, or as shamu suggested, 2 100's. If you are going to be getting live plants, i would suggest lighting that would equal 2 watts per gallon. For the 55 you would want about 110 watts. a little less is ok.