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DT Alpine III spokes are excellent, among the very best for your application. I've had zero problems with them. Sheldon Brown has written highly of them, and Joe Young (a great and very experienced wheelbuilder) recommended them to me.
Yes, I think an ace wheelbuilder is worth finding. They don't cost that much, even the best ones; and the added reliability is worth it. This is one of the most important things to get right, if you want reliability and the freedom from mechanical issues while touring.
Years of experience can really make a difference when it comes to mechanics and wheelbuilders. Some of these guys have seen so many failures and breakdowns, and the good ones understand what works, far better than the vast majority of cyclists and less experienced mechanics and wheelbuilders. Some are also very conscientious and perfectionistic.
These guys also know rims. If you give your weight, trip length, terrain, riding style etc., they'll recommend the most appropriate rim choices.
If Joe Young is still around, you could give him a call. He is a good guy to work with. Last I heard he was in Texas. It's easy to ship the wheels via FedEx. Gravy Wheels in San Anselmo, CA, used to be good. Don't know the current situation.
If you want to learn about wheelbuilding, there are good, detailed books by Jobst Brandt and Gerd S(c)hraner. I woul still recommend a crack wheelbuilder, though. They'll have some extra levels of skill and understanding compared to anyone doing it for the first time, even with these books and other resources. Some people do it themselves and it works out fine. I would still recommend an excellent builder, though. Along wth understanding as much of it as you care to go into.
Another approach to finding ultra-reliable rims is to see what companies like Co-Motion use on their tandems and touring or touring-expedition bikes. They have a ton of experience with many high quality builds, and a wide variety of riders -- they've seen a lot and know what works. Same for other longterm high-end, quality tandem builders.
Tandems see extra stresses, especially touring and expedition tandems; and these setups need an extra level of reliability. You might not need to go all the way to the end of their spectrum, but they might have some good recommendations or indications for you.
Downhill mt biking is another field where you will find exceptionally strong rims being used. Mtbr.com reviews might be of interest.
In general, the narrower rims are not as suitable as the wider ones for your application. Someone like Joe Young could explain this well.