The issues I can foresee on a tour like the OP plans relate muchly to bearings, brakes and spokes. If you have the tools to cope with adjustment, cleaning and rebuilds in those areas, you will be OK. The rest really can be handled by a multitool.

You will, however, have to give thought to how you will remove the cassette in particular. Personally, I find replacing a chain whip with a piece of nylon strap (as used on bags and such) wrapped around the cassette and tied off on an adjacent spoke works well, and is compact and easy to stow, and has other uses if need-be. I am not sure of how readily available cassette cracker tools are these days -- mine was lost in a bushfire.

Incidentally, it is very easy to leave an item from a separete tool kit lying on the side of the road. I've done it with tyre levers and such, and it does take an organised mind to ensure you replace what you have used or removed from your tool pouch or whatever you are going to carry it in.

It can be said a multitool can also be left on the side of the road, but it is a relatively big item, compared with singles of its components, and really cannot be missed in a tool pack because of its weight.

And, I have stripped down and rebuilt bikes with multitools often in the past, with the exception, of course, of the bigger components such as quill headsets and BBs and cone nuts. I can't say that using single tools for the same work is any better, to be honest. The quality of the fit of the hexkeys is important.

Has the OP given any thought to what the tool kit shall reside in? I have found waterproofness is very desirable. I use a small Sea to Summit dry bag so that I can put the last fold of the openilng through the rails of my saddle and clip it off there. Handy under the seat, but out of the way, and waterproof. Obviously, the kit is small, and includes a multitool...

On my first major tour, I didn't know much about bike mechanics, so I took along a nine-inch shifting spanner (crescent wrench), and various other sundry items. I survived but not without dramas.

Thanks for posting, as I am gong over the inventory for my extended trip, wondering what I need and don't. I must not have put the "right" key words in, as my search of the forum revealed nothing.

I have done small trips with a small set of tools, but branching out and extending the trip, I have thought of using Murphy's law and the old biker creed, if it can go wrong it will, and if I don't take an extra tube/patch kit, I'll have a flat. Out on an extended tour that could be anything, so one has to think practically, and what I can fix that would get me to where I can get the repair I need. That shortened my list a bit.