Im not sure what you mean by a custom water loop, Like i Said this is all new to me, im thinking maybe radiator on one side and the piping going to the other side. I guess that would be a custom water look wouldnt it.
i didnt know you could cool gpus now, only cpus. I might need to rethink this now. As for tubing, well Clear tubing and so long as it stays in place and cant get leaks or break over time from wear and tear is what i want. Idk what you mean by fittings.