probably the best tubes for now are 1/2"
Trustable brands are swiftech, dangerden and uhh thats all I can reall aTM.
Best site to buy from: www.petrastechshop.com
these guys know what their doing, I Even spoke to the owner in person lol, great guy, great prices.
a radiator is simply the "Heat core", where the heat that the water transports from your CPU/GPU will dissipate from the water [Without that, the water will first cool the CPU and GPU by absorbing the heat, but then they'll reach the pump and will just circulate again on the cpu and gpu and get hotter and hotter]
You can tell by the maximum head room [thats how theoretically far the pump can push water in a 90 degrees] and how many liters per hour she does, a good head room is 10feet [3meters] and above, and like 1020+ liters per hour. Also, a good pump can be rated 'good' simpley because its very silent and don't do much vibrations..... but thats a matter of perference, some people just don't really care about noise.
Here is what I'm going to order in hte next few days from the exact same shop, this is under a very strict budget of 200$ [sums up for 226$ with shipping]:
MP-1 CPU block
Black Ice Pro 2 radiator
Swiftech MCRES-MICRO Reservoir
I hope this will help you