Thanks again for all the input, really appreciate it.
As for the NH-D15 fit, yeah I had considered those extras just wasn't sure they'd equate to 2 cm + that YouTube video gave me hope. If I was building the system myself I would buy the MB and the D15 first and see if they fitted, but as I'd be sending the case off to have the components installed, that's unfortunately not an option (buying from these guys most likely:
https://www.pcspecialist.co.uk/). Fairly annoying that it likely won't fit as one of the reasons I bought the thing in the first place (aside for build quality/looks) was the "I won't ever have to worry about what I put in it" factor. That was at the time when graphics cards were getting bigger and longer. Oh well... It looks like Lian Li might have something suitable without busting the bank, but only just started looking.
As for the look itself (Noctua), I don't mind it, personally. Especially for an old school workstation, sans RGB. I can see how the DRP4 would fit much better in an all black rig using RGB though. My current case (bare aluminium, in and out) doesn't have a window, so how things look inside isn't a big concern, that said some of Gigabyte's offerings are pretty fairground (to me) and I can't help being put off by the looks, even though that's pretty ridiculous given my situation! I hear the AORUS Master is a good board, on par with the Hero, but offering a third M.2 and WiFi (for the same price as the 2 M.2, non-WiFi Hero). Would you agree that MBs in this range are what I should be looking at? I believe that was the consensus on the first page. Whilst I won't be overclocking, I do value high grade components, particularly as the machine will be seeing heavy usage.
Regarding 3ds Max: As I understand it Max doesn't really make much use of extra cores except when rendering when they then admittedly make a huge difference. I do very little rendering, primarily lighting bakes, so this isn't of high importance to me. As mentioned, I did consider HEDT, specifically the 12-core part, but opinion seemed to be that Max, Photoshop and games would all run better on the 9900K (aside from rendering!) and that the cost couldn't be justified. If they were the same, or similar price I'd likely go with the HEDT solution, regardless of the slower speeds (though not inconsiderable); the 18-core part suggested is way out of my price range though. Plus, I don't think I'll need 128 GB RAM, 64 should be more than sufficient. Again, if money was no object, sure it'd be nice to have that option, just in case, but I think I should be fine (famous last words!).
Speaking of RAM, I'll consider going for a faster option, dependent on cost and provided it doesn't introduce instability (5% faster, in some apps only, but the odd crash/issue isn't worth it to me). The price difference between 2666 MHz and 3000 MHz is £60 at PC Specialist. Though they don't offer any above that in the 64 GB config, am sure I could order some if needs be. Agree that £60 isn't all that much in terms of the full build, but it keeps going up and up... I was originally going with a cheaper MB for e.g., thought I could use my existing case and so on. I'll likely nail everything else down first then see where I am with the RAM.
Thanks once more for taking the time to help.