Need help with fittings

Hello, first time doing a custom liquid cooled system. I know I wanna do a 360rad, would like it to be the thicker rad too. However I can not for the life of me keep up with all the fittings I need. I would like to have as much flow as possible. I'm not worried about the number of fittings I need just the type. I know everything is usually in g1/4 threads but do I need barbs or cupplers, and do they come with the collars to tighten down. I basically need a fast lesson in liquid cooled fittings. There are just so many types with some in mm and some in inches while I've also seen cm, it just makes me drunk feeling just looking at it all. Is there any shot someone could kinda simplify things for me please? Or possibly anywhere that sells a lot of the hard line and fittings? I can source the water block, rad, and pump. I just need help with fittings more than anything.