Hi an welcome to SD pieky!
I see ya want to start a 55G with plants...I am hoping that you will be starting this tank with 4-5 Discus a lil larger than juvies.
It is hard to grow out juvies in a planted tank due to the fact that you have to feed them so much. The amount of feeding requires alot of WC's which would not benifit your plants!
The heater an the filters look good. Carbon filtration depends on what you want to do with your tank. Reading that carbon is not good for Discus probably boils down to growing out juvies in a BB tank. Read this.
http://forum.simplydiscus.com/showthread.php?t=28937
If you want to start a planted tank with adults or close to adults then what you have will work ok.
For a lil more info on the subject read these.
http://forum.simplydiscus.com/showthread.php?t=59346
http://forum.simplydiscus.com/showthread.php?t=55440
hth
Mark