Small observations from building today...
There is no hecking way you are fitting more than one 3.5" hdd if your PSU is modular. Maybe it's viable if all your cables come out of one corner, but if the front of it is covered in sockets and you use them... well. Sorry for the cable clutter (but this is part of the point) but you can see the hdd. There are technically 4 positions for the caddy, but if you want 2 you'll have to use the left most and the right most. Yes the black "shadow" on the right side IS the PSU. There is no space for cables to come out of it if you put a drive there.
It is possible to mount one of the caddies upside down on the underside of the shroud - however it is horizontally aligned with the first screw point underneath and therefore shares exactly the same problem. Unless your modular PSU has all the cables at top or bottom, you cannot put a drive here.
I will say; this isn't a problem for me personally. I only have the 1 spinny drive, and now that it's in, I have realised it is the loudest thing in this case when at idle. Hard to overstate how absolutely silent this PC is from 3 feet away, and I'll put it on the floor so... yeah. Never have I had a stronger desire to swap that last HDD out for an SSD. Soon as 4tb drops close to £100, I'll be rid of this old clunker.. Won't need a fast drive, it's just big media storage (there's a 2tb sn850x in here for my speed needs).
I'm also struggling a bit for how to deal with the CPU cooler's RGB cable clutter. I've had to settle for just using a couple of white twisty ties to keep them together, and hold the shortest one against the lid. Part of me is wondering whether I'm man enough to disassemble the whole thing, snip the cable and take a few inches out, but that's probably too much effort.
Other than that, the cabling is by far the best I've ever managed
Still in my spare room with my backup GPU in it, but the 3.5 and 2.5 drives are in so the back side of the case doesn't need to come off again. Viewed from a normal angle, the cable clutter just won't be visible - I love this new trend of the PSU shroud for the lower section and I feel like Fractal Design were on point with the dark grey internals so the LEDs I have don't glow it up excessively. I may turn them off, may not, we'll see.
Still need to move my proper GPU, m.2 games drive, and Soundblaster Z from the old PC. I have a hunch the red lights in the Soundblaster are going to annoy me, but that's ok - there's a really good youtube video on how to take off the shroud and either cover or snip off the LEDs completely. It looks very simple to do and the card is well out of warranty anyway. I don't think I can even be bothered to try the sound on this motherboard (Asus X670E-A) because experience suggests onboard has never, ever competed with even a budget Creative card.
Edit: no, the Peerless Assassin absolutely will not fit on top of LED ram! I didn't know this when I bought it, but got lucky because I'd spotted these "low profile" G.Skills on a decent offer a few months back. It is however drop dead quiet once you throttle it to about 60% in the bios. I wasn't expecting to end up with a silent build, but I keep forgetting that I've left it on and it's only when I turn the lights off to go to bed that the LEDs remind me. The graphics card will be by far the loudest part when gaming.
Edit 2: I'm currently reading up on whether any of the lower 3 m.2 slots are the "best" place for my old 1tb Samsung 970 Evo. I suspect that with X670E nothing ends up halving in bandwidth, or if it does, it'll be that bottom 4x PCIE slot which I only need 1x of anyway because that's where I'll put the soundblaster. Although I guess one of these slots is direct to CPU, I'm not sure I should worry about that for a PCIE 3.0 drive?