this is better at the watercooling club thread.

CPU block : EK Supreme HF Nickel (This should be fine?) - why wouldn't it be fine? Supreme HF is one of the best cpu block.
Pump : Laing D5/ Swiftech MCP 655 (This should be fine as well?) - good pump. you might wanna try the one with variable speed.
Radiator: HW Labs Black Ice Xtreme 240mm (Considered the 360mm but dont think I can fit it in somehow?) - 240mm rad should be enough for processor only loop, might have problem with internal mount.
Tubes : XSPC 7/16ID - 5/8OD (Radiator barbs are 1/2ID but I want the tubes to fit tight. Or you suggest I switch to 1/2ID tubes?) - i'd go with 1/2"ID tubes, get clamps or zip ties.
Coolant : Distilled water(Feser Aqua) + Biocide from Petra's Tech - just get tesco distilled water and biocide. feser water is just expensive water.
Thermal Paste : Arctic Silver 5 - no comment, but supreme hf does come with thermal paste. mx-2 if i'm not mistaken.