INCOMING ESSAY
You're about where I started with my loop. I started out with an XSPC-assembled kit, that included the Raystorm block, D5 Vario pump, dual 5.25" bay reservoir, compression fittings, and tubing. I later added the EK FC R9 290X block/backplate for my GPU, and a second radiator. Then I changed all the fittings from the XSPC ones (which had a diamond-pattern knurling on them that was just awful) to EK ACF fittings, and changed the bay res to an EK DBAY Res MX (I ended up stripping the acetal threads on the XSPC res, but the EK one is a bit higher quality, better dampened, and looks better). My Raystorm block (after 2 years) has stress cracking on the plastic mounting plate, so I'm soon to change that out for either the newer Raystorm Pro, or an EK Supremacy, which have aluminum mounting plates.
Now to actually answer your questions :)
As SoulFallen said, you're only going to find aluminum blocks/rads with real cheap products. Copper and aluminum connected by an electrolyte (water) creates a galvanic reaction, which can short the components blocks are mounted to and lead to corrosion of loop parts, which is obviously undesirable. The XSPC rads you're looking at are copper. I have an EX280 and EX140 in my loop, and they've been great for me. Particularly because they're pretty slim, which is good for my case that was not at all designed for custom loop. If you have the space to go with thicker rads (especially a thick radiator with push/pull fans), then I'd do a cost analysis on that because more fin area always helps with heat dissipation.
For me, there's only really two pumps to chose from, D5 variants or DDC variants. There's plenty to read about online about the choice between them, but I'd say unless you're constrained for space, get yourself a D5. They're powerful, quiet, and there's a ton of pump tops and reservoirs for them.
For fittings, I recommend compression fittings just because they look nice, and are potentially more secure than barb/clamp style ones. But either way you need to be making clean, even cuts with a sharp tubing cutter to prevent leaks. For compression fittings, make sure the threading is smooth and the knurling goes in one direction. Fittings that cross thread, and knurling that tears up your fingers make loop maintenance way harder than it needs to be. Make sure not to tighten fittings into your acetal block (or plastic other parts) too tightly, because you can (and with repeated reassembly, will) strip out the plastic.
As far as coolant, ask 100 people and you'll get 100 different opinions. Part of the equation is your tubing, and how you prep the system, so I'll cover that first. I recommend Primochill Advanced LRT tubing, because other types of tubing can contain plasticizers that can leach into your coolant and cause a murky, undesirable appearance. For system prep, you really only need to focus on the radiators. They often have residual flux or machine debris from construction, so the general consensus is to flush them with a 20% white vinegar/distilled water mix before use. Some people recommend just a flush, some recommend an overnight soak. It's your call, but very extended exposure to vinegar could (probably unlikely) damage the rads. I overnight mine, and they've always been fine.
If you want a colored system, the easiest way to do it is just with colored tubing and distilled water, with a silver piece in the loop for biological inhibition. Oxidation of your copper blocks is going to be inevitable, but fortunately it's really only an appearance problem. You'll probably have to disassemble and clean them down the road.
Now, I'm the type that likes clear tubing with colored coolant. But I'm also the type who's had to spend two days cleaning purple particulate matter out of their blocks, radiators, and reservoir ¯_(ツ)_/¯. That being said, the EK EKoolant Blood red that I've been using since then is the most stable (colored) pre-mixed coolant I've ever seen. Nice stuff.
The size of radiators you've picked should be more than enough, depending on how big you loop gets. I use my 280+140mm rads for essentially an FX-9590 and OC'ed R9 290X (read: HOT parts) and it's been fine.
