Cool project!
It's great that you can make the change slowly.
A couple of things that come to mind.
While the Remora Pro may be fine for the bigger tank ( though it is rated at 75g most manufacturers overrate their skimmers.) I would plan the sump based on the theory of upgrading the skimmer somewhere down the line. I love ASM slimmers and a G2 sounds perfect. You could go with a G1x but the price difference is minimal so I would go with the bigger skimmer. Even if you leave the Remora on you will still get the benefits of the water volume and you can likely fill the area with cheato or something in the meantime.
Particularly if you are going with a sump/fuge combo then I would get the biggest tank that will fit under the stand and still give you some space for cleaning and adjustments.
As to the power heads you may want to look at the Hydor Koralia powerheads. I have two that arrive today so I'll let everybody know my experience. Those that I have read have been excellent. Several people though have traded in for a smaller model because they were just too much flow. Makes me nervous about my 2 #4s that get here today.
That's enough for now. I gotta get to work.