GP1

2wpg will be fine for those plants except for the hairgrass which you probably need more light for.
Yes the T5HO will put out more light per watt than CF's & will run cooler.
If you are using Excel then you should be able to use the T5HO's that you have. Excel is a liquid form of carbon that is supposed to be used instead of injected co2, so you shouldn't have any algae issues from lack of carbon. Personally I would rig a DIY co2 system though as if done right can provide fantastic results & cost you heaps less than Excel will in the long run.