If you wanted to do a custom loop the best place to start is a complete kits like
these. You'll probably have to buy extra stuff too, that's just the way with custom kits. It gets expensive. It's also a fuck around and needs much higher maintenance than air or aio coolers. Basically unless you genuinely enjoy working on your pc and are prepared for the extra work, I wouldn't recommend it. The performance boost isn't that major either unless you plan to really push benchmarks. That being said if you want to pursue it i'd be happy to help, it is rewarding to do.
Aside from that i'll second the corsair h100i but I know little of the krakens performance personally.