The light fixture you selected is basically the same one I have, just different brand (coralife). You should be fine with softies and most LPS, just try to place most LPS in the mid to upper regions of the tank for best results. I would change the bulbs out after they are about 7-8 months old as mine are at that point and seem to have shifted spectrum/color a bit. Just use your current light until you get coral then stick the new light on to save bulb life.
I would go with the Aqua-C as the Coralife Super Skimmers (CSS) suck from other peoples reviews and experiences. Reef octopus and CPR are other brands that make good skimmers for a good price. There are many crap skimmers out there like the SeaClone (sadly I got one...) and the CSS, so beware of what you are buying.
I would just grab a liquid test kit next time you head to the pet store because it is easier than running to the store every time you need to test parameters. If you decide to buy RO water, make sure it is actually reverse osmosis instead of the typical carbon filtration system that many stores have. Also use the 5 gallon jugs instead of the 1 gallon ones if you don't get a RO unit, just easier to haul than 10 little jugs.
I would go with the koralia 1's for powerhead, and get 2 of them. For future reference, you want at least 20x-30x turnover per hour in you tank. I have 2 koralia 1's in my 20g and I like them.
Hope this helps.