Yeah, RO/DI is all new to me as well. I plan on buying dry rock rubble from bulk reef supply for my sump.. You should check them out, they have good prices.
Halides are unnecessary for the sump you're not going to have any corals down there. I'm running a daylight 100 watt equivalent fluorescent bulb (screw-in) on my 20 gallon long sump, and my chaeto is really taking off; it also worked pretty good for the mangrove propagules I had in there before I had to remove the DSB.
You could probably stick the live rock used for seeding the main aquarium in the sump after it's seeded the main rock structure if you want to make all the rocks match in the main aquarium as well as avoid having to buy more rock for the sump.
Also, be sure to keep the pump's gph under what the overflows can handle; that's really the main restraining factor when it comes to the pump.
if i were you, i would just wait and buy it all at once. Alot can happen in 18 months if i read correctly. Price drop on items or better equipments or updated versions of it can be released etc etc.
Ok, thanks. I will look into those. I would much rather have something built for quality and that will last a long time over trying to save a few bucks. Someone told me DANNER Mag drives are good as well. Any experience with these or no?