As with any forum.. you will get multiple views on resolving the same problem/decision, and you chose what best suits your needs/skillset.
Your choice on ATX board is fine. The ASUS 1150 Maximus is good ...I put a choice in my post earlier, on looks versus all in one on the ASUS package. Did not mean to mislead you into doing research for a larger board.
My question on size was more to do the with the case, as I didn't know CaseLabs didn't give choice of XLATX or HPTX motherboard tray on TH10. They give this choice on STH10.
If you put a drain on the lowest part of your loop...preferably each loop has at least 1 radiator in the bottom, you can take one of the AMS Radiator ports to connect to drain. But you have to drill a hole, its easy.. I put a guide on that in my STH10 build. If you do this, and you are using Distilled water, you don't need QDC's. Draining takes 5 mins, refilling another 5 mins, and I didn't have to re-bleed the loop. Did this few times on the STH10 build. Distilled Water is the best - can't go wrong with that.
If you want to go basic tubing. I would recommend you copy theSeekerofFun's tubing scheme. Black Tygon Norprene 3/8" and 1/2" OD
with White Monsoon for cold and Black Monsoon for warm water. Its simple, easy to disconnect (don't tighten too much with the tool that Monsoon gives you)... Don't go larger that 1/2" Fittings, as with AQ parts you may have issues near their G1/4 ports.