The main difference between D5 and DDC pumps is size, DDC are smaller... However DDC pumps also have had problems with reliability in the past. I have one of both and both work great. As for the backplate, you can use the stock one in conjunction with the FC block. You would probably benefit the most from a minimum of triple spacing radiators, as for reservoirs... the more water in the loop, the better though the radiator can only cool so much water at a time. Surface area is important for efficient heat dissipation. In some cases (between looped GPUs or if you dont put your mosfets last) a buffer( a small radiator(120mm)) can give gains in heat dissipation
Coolant comes down to how often you want to pull your loop apart for cleaning. As in coolant with dyes tend to eventually coagulate (the dye has to come out of suspension at some point) at critical points in the loop. There are performance based coolants that might offer advantages over pure distilled, but the gain is minimal compared to the extra effort (and money) you'll expend cleaning and maintaining. I go with pure distilled water with a biocide added to keep the nasties dead. Anti corrosion agents arent necessary if you arent running any blocks with aluminum or mixing metals. An old trick to use for insane runs is to freeze up some distilled cubes and drop them in the reservoir...just be wary of temperature differences/ components with possible high cold bugs/ and as always condensation, though condensation is is pretty low risk with chilled distilled.
What kind of fans and what rating depends on the radiator you choose, as some are optimized for low airflow conditions while others cool better with high CFM fans.
Once you have the parts ready, then comes plotting the loop order and placement...which is easy if you do a little research (which I know you will). I hope this helps and Good luck!!!
