Harritaco - Your loop looks fine. As far as how much you need? A 360 will take care of a cpu and single gpu, but a 360+120 will do an even better job. If you are worried about air intake into the case look for vented optical bay covers. If you are willing to mod your case I would see if you could get a 3x140 up top. 140 mm fans will be quieter than 120 (for a given airflow) and a 420 rad would be all you'd need.
Also consider rads like the SR-1 - they work better with low speed, quiet fans than the denser ones.
Just be very careful and extremely thorough when you put it all together. Leaks will ruin your whole day. If you go with barb fittings make sure the tubing goes all the way to the base and put something on them - like zip ties or hose clamps.