Not to be a broken record of GingerJohn, but his recommendation of a better pump is solid. I've got a HAF-X with 1 6950 block, a relatively restrictive CPU block, and a dense radiator and I've had no problems with my MCP355 with XSPC reservoir top, and could recommend it in a heartbeat in a HAF-X.
The only issue you might run into in the HAF-X is with radiator height. I've got a pretty thick radiator (HW-labs GTX360), but it's still a few mm short of the RX360, so I can get 38mm fans on two of the 3 fan spaces, but I don't think you could do that with an RX360, you'll be limited to 25mm fans, though that isn't really a problem. You can go with any radiator you'd like really. Here
is some great info on choosing the right 360 rad for you, and remember that all of them will fit no worse than an RX360, but an RX360 has great performance at lower fan speeds. I've got 2200rpm fans on my GTX360, and unless I'm folding or gaming, I never hear them (they're on a temperature adjusted controller through PWM signals from my motherboard, which I HIGHLY recommend using). The 200mm fans are now louder than my radiator fans when I'm not doing something processor intensive, and the 200mm fans are pretty quiet. I regularly hear my harddrives spin up and wash out the sound of the fans; It's pretty awesome...
I'd recommend adding Primochill Primoflex tubing, and fittings are up to you. I went on the less expensive side and did all 1/2" barbs with worm-drive screw-down clamps with 7/16" ID tubing, which will be tighter on the 1/2" barbs. If you can afford compression fittings, they look better and hold better than barbs by themselves.