Thanks for all the detailed replies.
A few things which might help explain my choices:
RAM:
The difference between 32 GB and 64 GB is £153. Total system cost is between £2,600-£3,000, depending on the configuration. Various articles I've read all point towards more lower speed RAM being preferable to less high speed RAM, bear in mind I will not be overclocking (also recall that 2666 MHz was the max speed that RAM would function at if not overclocked, though could be wrong here). I work with very large Photoshop files (.psb format), some at ~8 GB in size; that's 4K texture source files. I will be increasing these files to 8K, so x4 that (or rather new textures will be mastered at this size). I also run 3ds Max and frequently have many browser tabs open for research (30+ not uncommon). Whilst I'm sure 32 GB would be absolutely fine for now, 64 GB is basically just "I never have to worry about it, full stop" territory. I also do not want to go down the route of "I can add more later" as have been burnt in the past (the exact RAM I needed became close to impossible to find and was insanely expensive when I did locate some).
In summary: Very heavy PS work, coupled with Max, lots of tabs (+ other image viewing progs). Future-proofing/forget entirely about any RAM issues. Price difference not bad when considering entire system cost. Faster RAM often makes v. little difference/more for very specific programs and/or for those who enjoy tweaking/overclocking for the fun of it (please correct if wrong, but this is what I've read).
CPU:
i9-9920X is too expensive and clocked lower (4.5 GHz vs 5 GHz), in addition I don't do a lot of rendering, mostly modelling (real-time). i9-9900K is the fastest you can buy (but not insanely priced like some of the HEDT solutions) and I want the system to last. I will not be overclocking it and thus thought a high-end fan would be sufficient. Thanks
Darkbreeze for pointing out that the Noctua NH-D15 would not fit the case. I'd not given this much thought as I just assumed "this case is a beast, one thing I don't have to worry about is space"
. I'll look at Noctua's other solutions, any you would particularly recommend? Water cooling worries me, as I'm not a pro so just want to be able to set it up and leave it (for life). I'd thought that a top-of-the-line air cooler would be sufficient in an airy case if not overclocking.
I am not a fan of AMD. Maybe this is unfair these days, but I had a bad experience in the past where the eventual solution was to cut my losses and switch to Intel and nVidia. Admittedly it was a while back, but it was a case of on paper both the CPU and GPU trumped the Intel/nVidia offerings (and thus were the solid recommendations online) but in practise I had all sorts of issues. Maybe this was due to my programs (Max and Photoshop primarily), but I recall having problems with games too which I think was due to poor driver support. Also the industry (games dev.) were almost all (where I worked at the time, and previously) on Intel/nVidia setups. Just seems like a more stable/professional choice, especially for people such as myself that don't want to tinker with things or spend time troubleshooting issues. Quite possible this has all changes now, but it was such a bad experience I'm not willing to risk it, particularly when currently the Intel/vNidia offerings are still the best option if price is not the deciding factor.
GPU:
As mentioned I do find the price of the 2080 Ti to be pretty ridiculous, but looking at all the benchmarks it is significantly faster, particularly at 4K. I'm not going the Titan or Quadro route. Card needs to perform equally well in Max and games. As with the other components, I want it to last. I also think the extra memory might be of use for my needs (11 GB vs 8 GB).
Motherboard:
From a non-overclocking perspective the Z390 Maximus XI Hero (WiFi) or Aorus Master seem to be the best. I prefer the look of the Code to the Hero, hence why I included that, and prefer the look of the WS Pro to both (unlikely to go with the Pro however due to the extra cost and no WiFi. I like the utilitarian look, but not that much
). As you can probably tell, I'm not a fan of RGB lighting and flash designs. With that in mind, you can prob see why I am not leaning towards the Aorus Master; though on paper I have to admit the specs look good, it's a real eyesore IMO (am sure others love it, just my opinion). Then again, it'll be in the case and I don't have a viewing window, so...
I believe utilising two M.2 drives loses me 2 SATAs, but most of the boards mentioned have 6 SATA slots (I think) - I will check again.
Case:
Not certain on this yet, but my thoughts with sticking with the TJ07 were that in the £200-£300 price range most of the other options are not of the same quality and/or I'm not a fan of the styling. Looked at the Obsidian 750D and some other similar designs, but there seem to be build quality issues. Also not keen on plastic masquerading as brushed metal. And finally... it's an extra £200-£300 on top for a case which I'll likely not like to look of as much as the TJ07. Going by my other choices you might think that money isn't much of an object with this build, but it is still a factor; bear in mind I want it to last and am not intending to replace it 2-3 years from now hence the selection of top-tier parts across the board.
I will re-read all your comments above again this evening (no time now, unfortunately). Would really appreciate any more thoughts, all very helpful indeed. Sorry for the wall of text...
Thanks again.