Hey Bone! Thought i'd chime in as you're well aware I've just been through all of this myself
I can't vouch for the Barrow fittings, never knew they existed. but I can say that BitsPower and EK Fittings are very good.
PETG 12/16 tubing looks very nice, that's the same tubing I've used in my build. - however I haven't been able to find an inner silicone rubber that properly fits the inside 12mm of my PETG tubing!.. this is VERY frustrating, because any amount of space that you have between the silicone rubber and the inside of the PETG tube will translate into your bends being slightly collapsed and flattened a little.
what brand of PETG are you going with? I'd be very interested to find out if your silicone inner rubber is a tight fit in your choice of PETG or not.
Radiators - I have to admit, I'm not 100% sold on the EK brand of radiators, my EK CE420 feels a little flimsy, and the screw holes on 1 side will not thread... it's as if the holes are ever so slightly too small for the included screws? I had to use thin cable ties in the end.
My front HWLabs Black Ice Nemesis GTS 280 radiator though is AMAZING, I love the build quality on this thing!
Front Radiator - Be careful with your choice of front rad, have you measured the size of the gap between your HDD cages and the front of the case yet? - I am currently running a 30mm Radiator in the front and I can see that there's space for maybe another 10mm, so I reckon a 40mm Radiator in the front would just about fit... however i'm not so sure about your chosen 45mm NexxoS XT45 rad.. you better measure the gap before you go ahead and purchase this one.
Top Radiator - you will be able to fit a 420mm radiatior in the top with the drive cage still attached, your optical drive will have to go into the bottom slot of course... however I ended up removing my drive entirely because I literally haven't used it in about a year. I decided that i'd just grab an external USB ODD caddy if I ever need to use it.
your water cooling loop diagram looks fine to me, in fact it's exactly the same as my own loop diagram so no complaints there!
Just remember to factor in a drainage port and a fill port (I forgot, and had to pull the system apart to add one.) - I see you've already listed the multi-port top so that will help a lot with filling options
As this is your first build here are a few pointers: (I apologise if some of these are obvious)
- When filling the loop, make sure you open up a spare port on the reservoir to let the air out of your system, filling the loop without an 'air hole' makes is harder to bleed the air out.
- Make sure all your ports are plugged before you turn the system on! - this should be obvious, and I don't need to explain what will happen if you don't!
- contrary to the above, DO open 1 port to allow the air to bleed out whilst you're filling/power cycling your system. - I used a tube attached to the top of my reservoir, connected to a funnel, allowing me to let the air out and simultaneously pour more liquid in as needed.
- Hard Tubing - measure twice, bend once. - you want to try and get those bends set on the first try, if you have to re-bend/un-bend a bend (so many bends!) then it'll start to look a little warped unless you're careful.
- Practice practice practice! - it's a good idea to practice getting the bending technique right on a piece of tubing first, it took me about 12 bends and 2 days of attempts before it clicked and I figured out how to make perfect bends.
- cut sparingly - always make your initial cuts too long on purpose, the idea is to get your tubing as close to the correct length as possible.. then re-measure the tube and cut small bits off until you get to the correct size. - the last thing you want to do is accidentally cut your tube too short after you've spent all that time making the perfect bend!
- Always buy more tubing than you need! - if you think you could build the system with 4 tube lengths, buy 8! - trust me you'll need some tube to 'practice' with, and you'll definitely need some tube spare for when you inevitably mess up (i screwed up cutting, I screwed up bends... I went through about 6.5x 1000mm tubes before I finalised my build)
Of course if you decide to go the soft tube route, then you can ignore half of this! - soft tube is SOOO much easier to work with.
That's all for now, if you have any more questions, or if I think of anymore pointers, i'll reply back