Does it need to be pretty, or just work? That can make a big difference in the initial price.
Regarding fittings, cpu loop is easy to do without any angled fittings, but with gpu involved, you should also get a couple of 90 degree fittings to spare, just in case.
A small (150ml or so) tube res is usually the most convenient option as far as tube routing and filling goes.
As for the pump, I got an
EK DCP 4.0, which is pretty straight forward as it doesn't need to be mounted anywhere and can sit by itself on the bottom of the chassis. It's also more affordable and you won't need to worry about getting additional pump tops.
Distilled water + biocide/kill coil makes maintenance easier and you don't need to worry about the dye building up anywhere or staining. If you want colors, get colored tubing.
A 360 45mm+ should be sufficient, paired with some 1200rpm fans.