If you ever plan to move on to primarily SPS corals, stick with the T5. If you're gonna do the softie/LPS thing and don't mind the initial setup cost of the LEDs, they are a nice option to reduce consumption and waste heat.
Depending on what supplement you use , there are calculators out there that will get you in the ballpark. Id recommend upping your alk a little bit, because if your pump fails you get out of spec and start losing stuff like me
There's no point to running rodi then. You're removing some particulates and VOCs/chloramine with the carbon, but everything else is going back in that would normally be taken out.