Consider a multi port top for that res. I have one on mine, much easier to fill + pipe up.
https://www.overclockers.co.uk/ek-water-blocks-ek-res-x3-multiport-top-wc-831-ek.html
https://www.overclockers.co.uk/ek-water-blocks-ek-res-x3-internal-tube-12-16-40mm-wc-837-ek.html
Any idea if these are compatible with this? It doesn't specifically say that it is in the item description but by the looks of things are lot of these EK reservoir parts look to be somewhat interchangeable?
I'm also putting together my first ever loop hence my noob question. And FWIW i bought Barrow fittings from Aliexpress and feel like quality items, not that I have anything to compare them to of course. You can get off Ebay too but they're about 1/3rd more expensive.