I can't think of a good reason for putting a bigger tyre on the front than on the back. In fact, I've done the opposite and put a slightly smaller tyre on the front on the basis that it carries less load than the rear tyre.

I was almost 70 when I first encountered tubeless bike tyres and am now a convert. A key requirement for a good tubeless experience is tubeless-ready rims. A good tyre-rim combination can be inflated with a simple pump. A poor combination results in much cursing and the need for a pressure tank. While tubeless tyres handle small punctures well, the ability to prevent a flat caused by a bigger cut is less certain and depends on the cut size and sealant. I've had one ride-stopping cut in ~20k miles which was caused by a flint shard. Attempts to plug the hole were unsuccessful so tyre boot and inner tube were needed.

Thanks for the link, I enjoyed reading that, but not as much as I enjoyed contrasting it with the piece on belts in Andy Blance's living with a Rohloff booklet, also available to download from the Thorn website.  On the same page he also explains why you're likely to get 20,000km + from an uncovered KMC X1 chain with minimal maintenance.  That's been my experience and is more than some of the Chainglider evangelists report.
When I first came across Thorn Bikes, in the late 90's, they stood out as having several opinions not shared by the rest of the cycle industry - Wheel size, disc brakes, kick stands, straight bars and later on belt drive...  I appreciate they're in the business of selling bikes, very nice bikes too, but they no longer stand out as being as different as they once were.
I'm curious to try a belt drive, just not curious enough to spend the money, for it to be to be economically justifiable it'd have to last me more miles than anyone is reporting they do.

I'm assuming from those numbers that it's 650B?  I think it would need to be pretty extreme before you noticed any benefit going over 54mm, that's already a lot of air, more than in the Sherpa. My Nomad on 650B 50mm tyres offers a very plush ride over just about anything I'd tackle. I'd be concentrating on the right tyre for the tour, rather than the width.  I know nothing of tubeless, I am curious to try, but for me it'd mean changing rims which I'm in no hurry to do.
Have a great trip.

In the article by Thorn I was surprised that they say that belts are more efficient than chains?

Maybe on aggregate if you're talking about a bare, dirty chain being ground into dust against a belt. My opinion is that anyone who's still running a bare chain on a hub gearbox might as well go back to the days of constant running replacement expense and maintenance work and filthy derailleur. I'm not impressed with test numbers taken on spotlessly clean components in a humidity- and dust-controlled laboratory.

In any event, for many of us who've given the connection between cleanliness and component longevity some thought, the real world is a Rohloff hub gearbox without derailleurs and jockey wheels (definitely the devil's invention), with the chain covered by a Chainglider. In this particular case, the chain is always run in near-optimal conditions and likely to leave an open belt for dead as the belt cannot be effectively covered, and its efficiency degrades as it gets dirtier. The Chainglider is the nearest thing possible to the mythical 'oil bath' of which gear heads' dreams are made.

A good quality Chainglider-covered chain basically operates on peak efficiency throughout its lifespan. That applies even if the chain inside the Chainglider receives zero maintenance. I've proven that by running my chains for their entire service life on the factory lube. (KMC has an especially effective and long-lasting factory lube. That is one reason I recommend their X8 chains so warmly.) That simple procedure, and the modest cost of about 50-60 Euro including delivery for a Chainglider increased my mileage per chain by a 160 percent.

Currently in Sri Lanka where my chain feels fine in it’s chainglider after 500 miles of gritty roads, I keep thinking I should oil it….

Jobst Brandt, an engineer who worked for Porsche, who don't hire idiots, where he designed the Grand Prix brakes, was an enthusiastic cyclist who condensed the engineering of the bicycle wheel into his book, The Bicycle Wheel, and devised the first bike computer, and brought slick tyres and many other revolutionary components to bicycles. I drove Porsche from the 356 series forward, so I was inclined to believe his obiter dicta, one of which was, 'The chief ingredients of grinding paste are dust and oil.' It's why I don't put any additional (to the factory lube) oil or grease on my bike's chain inside the Chainglider.

It is slightly ironic that Thorn do not make their bikes more compatible for chaingliders.   Certainly they were not enthusiastic about them when I bought one for my Raven……the problem being that the seat stays can touch the rear part of the chainglider and push it into the hub.  I started a thread here about fitting a Chainglider recently in the Rohloff section.

It may be that their later frames designed for a belt which is wider than a chain are more compatible with a chainglider?

In the article by Thorn I was surprised that they say that belts are more efficient than chains?

Currently in Sri Lanka where my chain feels fine in it’s chainglider after 500 miles of gritty roads, I keep thinking I should oil it….