If I'm buying from the UK, are there any weird fees I should be aware of? I know of import duties, but is there anything else that might suddenly increase the price considerably?
Does the $295 include VAT?
It doesn't include VAT, since it's shipping worldwide and every country has different VAT rates. You may be invoiced by customs to pay VAT and any other fees before the package is released.
Also, could those import duties be 'avoided' with some slight mislabeled parcel values?
Probably. This isn't an off the shelf product, whose price can be easily confirmed. But if your customs officers are clever they will find the real value and you may get fined for messing around.
Also very new to keyboards, so very unknowledgeable about most things. I've seen mentions of per-key backlighting. What actually is this? Is this just when you have switches with integrated LEDs?
I haven't yet seen any switches with integrated LEDs, but most of them have a little slot for LED mounting. You can pick up LEDs of your preferred color, nest them in the switches and solder them to the PCB. That's what "per-key backlighting" usually means: that the PCB supports installing individual LEDs. There are also PCBs that instead have SMD (Surface Mounted Device) RGB LEDs already pre-soldered where the keys would be. They can shine through switches if the switches have clear housings, providing you with a full RGB backlighting without the need to solder the LEDs. One example of such a PCB would be the Zeal60.
The photos of the PCB provided by senter show that it has LED mounting points, but no pre-installed SMD LEDs. Of course, if it did have SMD LEDs it would probably be underlined heavily in the GB thread, since it's an expensive and sometimes sought-after feature.
Really excited to maybe join this GB, if only I can decide what combination I want
There's already over 200 orders for this board. I don't think Fox Labs said there's going to be a limit on the production, but waiting too long might push you to the very end of the queue and a very long wait.