Depending on how deep you want to go, you could opt for one of the kits from XSPC. What size radiator is going to depend highly on your case. The HAF 922 will fit a 240mm length radiator, and how thick will depend on your motherboard. I have a RX240 radiator in my HAF 922 (thick radiator). The XSPC kits include everything you need pretty much including a bay reservoir, water block, tubing, barb connectors, fans but no coolant. My advice on coolant is to just use distilled water and a silver kill coil.
My Switch 810 has a RX360 and a EX240 radiator as well as 2 D5 pumps and is fully custom. So it all depends on how far you want to go and how much money you want to spend.