I would say "you're there".
Not that a single pump won't still work, it will, but you'll get almost double the head pressure with two and the security knowing that if one of the pumps fail, the second will still pump. I believe a single pump in the loop you described, depending on how many bends, would struggle in the long run. My two D5s, I purchase more than 10 years ago and they're still running great. My theory is because I always use them together, in serial. I could be completely wrong, I'm no expert, but I had a single D5 in another complicated loop and it failed after about 4 years. I believe the restriction of the loop caused that pump to work harder than if it had a second pump working along side it, hence the failure. I'm only sample size of one, but still, it was enough to convince me of two pumps in complicated loops.
I run two Koolance 480's, two RES and one GPU block and CPU block and always use two D5s in serial. I would say, IMHO, that when more than one Rad and waterblock is involved, two pumps is almost a necessity.
It looks like you'll have 3 RADs and 3 blocks. Again, IMHO, I would never run that loop without two pumps. Not saying it wouldn't work, but I'd sleep better at night knowing if one pump failed, I'd still be good to go.
Boy do I miss Martin's Liquid Lab......check this out for more info. It's old, but most of it still applies.
If you do go dual pump, GO SERIAL! Don't do a parallel loop.