Think it's time for a custom loop, could use some advice regarding mounting and connecting

So I've got a 5900x on a ROG Crosshair VIII Formula, with a zotac 3090 and it's all mounted on a Thermaltake P5

Now i was thinking a distro plate pump combo and a quad radiator. Leaning towards EK since i love the aesthetic and my mobo already has their logos on it

How do i go about estimating the connectors and tubing I would need? I don't look to go too fancy, soft tubing and the joints doing most the work would be fine

Also, from the videos online, and the fact my case is my room i was thinking of keeping the back of the GPU exposed for the sake of getting an active backplate at a later time. Online reviews seem to suggest that's a legit way to go

[Picture](https://i.imgur.com/ZVbiEqH.png) of Thesus for reference of layout, your help would be much appreciated :)