Full custom, would be awesome (I’d imagine) if done correctly. I’d expect the bike to handle like an extension of your body. However, which UK builders would you trust to get it right? There are alot of new builders in the UK, but I’d want someone with loads of experience to be translating your fit into a bike that rides as well as it could do. It could be complete bollocks though.
Also, ten years is ages to keep a bike.
The only material I would discount is Stainless Steel as I think it has all the disadvantages of Titanium (i.e. hard to work with, prone to breaking) and it’s also wafer thin so I’d not expect it to last long. Ti would be a better choice as it’d stand up to knocks better, plus you’re light and wouldn’t need the extra stiffness that OS steel brings.
If you really plan on keeping it ten years then get something with a good warranty. I mean who’re Ritte bikes? Will they even be about in 10 years? Enigma seem to do loads of Ti bikes and they’ve been around for a while.
Other thing is mudguards; the whole point of discs is for wet weather riding so you may aswell get something that clears them i.e. no 400mm chainstays.
I’d probs get a CAAD disc with 10 speed mechanical Campag (which coincidentally is what I ahve) 😀 Dream big.