Not a huge fan of the overall colour/appearance of the K10 QMK. I can't explain why, but just don't like it.
I am tempted by the K10 HE, but the shine through version looks weak? Barely shining through. Is there an option to only have one solid colour? I'm not a fan of RGB.
What's the difference between the switches used on the K10 HE and brown switches? The reason I have a preference for brown is the actuation force, etc. I find other switches, such as red, too sensitive.
I can be swayed to other options if they're similar to brown I guess.
Do you mean the one with the wood edges? Personally I think it looks great, but appreciate that's a taste thing. The 'normal' shine through version is just black-on-black, with shine through keycaps (I assumed when you said you wanted backlighting that you meant shine through, rather than just having PCB lighting with solid caps!)
QMK (aka VIA) is an open software implementation that allows you to configure the board from a web browser, so no bloatware (chromium, doesn't work with firefox... I use FF generally and only use it for this function, with QMK set as home page

) - It allows some pretty deep macro functionality, full programibility of every key and many options for controlling the lighting - I have my board set as static purple but pulses through other colours on keypress... you can just set it to whatever static colour you want.
If you're spending £100+, I wouldn't even consider anything that wasn't QMK and an aluminium frame.
HE switches are linear, like reds/blacks (blacks are a bit heavier than reds if memory serves), whereas browns are 'tactile' (they have a little bump to them but not as noticable as blues, which are 'clicky'), with the HEs though, they're hall-effect, meaning that they report how much they're pressed, rather than on/off. This means you can configure the actuation point, from 0.1mm to fully bottomoed out (~3.8-4mm).
It kinda depends how deep down the rabbit hole you want to go, there are thousands of switches available in linear/tactile/clicky, with different actuation forces/curves.
If you just want to buy a keyboard, and not accidentally acquire a new expensive hobby, then I don't think you'll go far wrong with a Keychron (as far as I've heard, they sound and feel lovely without any modification)
... a bit wordy, but hope that helps!