Please run clamps or something. The plastic ones are ocassionally underclamped, and can pop off if overclamped. The barbs you chose are just fine. I don't think any other parts have plastic. And 7/16" kinks easier. It's your money, so do what ya want, I really don't worry about it. I just say what I think is proper for especially new users, we want you to be happy. Do you want to ruin a Mobo? A PSU? Once your at it a while sure, but please run more than tight hose this time. You might do it wrong, no offense, but I've read about it more than a few times. Cutting corners with cost, bad advise, poor methodology etc......
Not a pain, it's fun. Open the pump inspect for 'stuff', mine had packing foam pieces inside, rinse out the blocks with hot sink water, then rinse with distilled should be enough. I should of opened my CPU block, it had a bit of gasket material in it, not enough to cause issues, didn't find it till my first full rebuild (Ever 6 months is recommended by many). The rad needs major cleaning. Fill with almost boiling water (sink water is fine) let sit 10 min or so to cool a bit, empty 1/2 out or so, shake like a crazy man for a few min. Pour it a glass bowl, if water has no particles, do it 3 more times, then rinse with distilled. Rince hoses and res too. Wipe hands with alcohol (keep away from plastics!!!) to remove oils on your fingers that will leave tarnish marks on the copper in a few weeks. Practice putting hose and clamps on, properly tightening barbs etc BEFORE you start putting stuff on the Mobo.
It's FUN, play with it, no rush. Took me 3 days to get my first loop up. It's a hobby and the experiance is meant to be savored.