Scott, two spares are ideal, but carrying then comes at a price if you are trying to keep the weight down. Your U1300 ambulance is pretty heavy to start out with, so unless you get rid of the box and start again, you will be travelling at close to GVM most of the time if you want to carry extra fuel and water, food etc. I said I was going to build everything super light weight, and I even used to weight each thing I added to the truck. Even with all that, I am close to my 7.5ton GVM when everything is loaded up.
We only have space for one spare in our design. We will look at possibly carrying two unmounted tyres on the camper roof when we travel around the world, but this increases our height to over 3.5m, so we will have to do some more research as to the availability of tyres in the countries we travel to. Everything is a compromise when you have a small truck like a U1250 or U1300.
Tyre sensors are a must, give you lots of warming that a tyre is losing air, and can help prevent the whole thing disintegrating. They also give tyre temperature, so you can see when heat is building up and you need to stop and find out why. Tyre patches, the proper ones for radials , not the tube patches and all the kit to remove and remount a tyre is essential, no matter how many spares you carry. We did a three month trip around Australia in very remote areas, three punctures in the same tyre, rear left hand side. We got a repair shop to do the first one after we plugged it with three tyre plugs so it would hold air. The next time we were close to a tyre repaired so got them to fix it, and the third one we plugged as it was just a nail. We decided to replace the two rear tyres because one had so many repair, and they were badly chipped. We run 255/85R16 on the Land Rover, and had to order them in especially for us, which took a week having to come from over 1200km away, but we ordered them when we were two weeks away from the place we got them changed.
If all else fails, then Fedex or similar will get you tyres in a week or two, but at quite a lot of expense. Like all things, how many spare part do you carry for the air system, cooling system, electrical system etc. We are after all driving around in 29 or 30 year old trucks.