Nicely done, but it's a shame you went through so much trial and error with your cooler and setup - wish I'd seen this thread sooner I could've chimed in!
I've gone overkill cooling my G850 with a Corsair H60 in my SG05 purely for the fun of it, but I've got it in vertically giving space for a full-length GPU if I want to later. For the hard drives, however, I took inspiration from Miahallen's MAX11L from a couple of years ago.
I have a Corsair Force 3 and WD Scorpio Blue mounted into an Akasa aluminium 2x2.5" caddy which is then mounted underneath the PSU - flip it over so the exhaust fan is pointing up and you have a perfect free space to mount the Akasa caddy.
I'm actually reworking mine a little though as I want to use the PSU support bar in my case which has a little lip on it about 1mm thick; there's also a similar lip on the back side of the case too where you mount the PSU. Currently I've just glued the Akasa mount directly to the PSU, but the lip gets in the way, so I'm going to rustle up some spacers about 1.5mm thick and stick them between the PSU and the Akasa mount.
No More Nails temporary strips are my friend lol hold 2kg of weight no problem, and the loaded Akasa mount is no more than 350g.
So yeah, flip your PSU, use a pair of 2.5" drives and you have all the space for a AIO water unit up front. Just lose the optical drive shelf.
Making that work is another story