I'm with the people who say you want to think in terms of something failing eventually - so pick your system to keep working minus any one component.
I've used the X-T1 and 18-135 in some pretty hostile conditions (airsoft skirmishes in the rain, for example) - and they worked out nicely, so I'd start with that combo, and plan to use it for basically everything. I really recommend the medium sized grip expansion with the 18-135; I find it rather unwieldy without. Also spare batteries, etc. Both of the above are probably available off-brand by now. Add a medium Gorrilapod and you've got some serious long exposure capabilities (it clamps to the handlebar of a bike lying on the ground rather nicely, for example), which means the only capability you're missing is low-light action, and ultrawide.
Everything else is your backup. Personally I'd get a second-hand X-E2, and a 35/1.4. The X-E2 has the same sensor, and is pretty cheap and durable - it's my suggestion for the cheapest/lightest available backup to your X-T1. Swap the 35 for another focal length if your "if I had to do everything with just one prime lens" preference is different, but given you listed it in both sets, I suspect it isn't. That's your low-light action lens, your "people" lens, your low-profile lens, and your "I could live with just this if I had to" lens.
I'd skip the ultrawide. It's a specialist, situational lens you shouldn't be using frequently... and you're trying to make a durable and flexible kit on a tight time and space/weight budget. If you can't do without, then try to squeeze it into your budget.
Buying the X-T1 and 18-135 new as a bundle, the X-E2 and 35/1.4 second-hand, a Gorillapod and some top-notch cards, plus off-brand handgrip and spare batteries... you should easily get change out of 2000 GBP. Think about bags. Personally, I'd expect to have the X-E2 and one lens buried in your bags, so get something waterproof to wrap them in, and use clothes for padding - and then the X-T1 with the other lens ready for action. If I wanted to keep it ready all-day, every day, I'd be using a Mindshift Ultralight Camera Cover (the "10" size fits that combo fine) and a really good strap to leave it attached to me and ready for action, but protected a bit from the world... but maybe you're a holster person, or prefer a small bag attached to your belt. Either way, I really wouldn't recommend a dedicated camera bag to hold all of the kit... unless that is also going to double as the thing you keep all your valuables in when you have parked up for the evening, and are leaving most of your kit in a hostel or whatever. I'd still pick it for that purpose first, and add a camera insert if appropriate.
Think about how you're editing and backing up photos as you go. A Nexus 7 or similar would be the lightest sane choice, connecting via wireless, backing photos up immediately, having respectable editing capabilities, and letting you upload everything to the cloud whenever you hit wireless. You'll want to upload to the cloud on a regular basis no matter what - but the tablet will let you post updates to social media, keep in touch with people, etc. (If you're expecting to take hundreds of photos a day, it will be too painful to edit on - at that point you're looking at an ultrabook ). TL;DR: XT-1, X-E2, 18-135, 35/1.4