First question to a builder would be how many weeks a year do you tour/when was your last tour. Next!!
I don't absolutely believe the person building has to be a tourer themselves. If you aren't you can't know, but the same is true about elite racing and most of the frame builders aren't elite racers. But at the same time touring is a subculture and I would probably deal with folks who are passionate about it if I could. If they are local but not around the corner, they might as well be across the country.
I would want to know what their touring concept is. Touring bikes are a really internally segmented category these days. The better bikes have a defining vision. So a Bike Friday is all about decent portability and decent riding quality. A Sakkit is mostly about expedition touring, though he covers the gamut, and about working from the load to the bag to the rack to the bike. The Thorn is about third world or back road conditions. The guy who just has a touring bike in the portfolio is probably, about slack geometry combined with some braze ons. There is a classic bike with a lot of junk on it like spoke carriers. I know some people like them, which is fine by me, but there is a caricature of certain features that add up to the bike that plays a touring bike on TV, but isn't for real. First, I want a bike that won't break any spokes; and second, if I do have to replace spokes, I want to start with clean ones.
I would seriously recommend getting The Beckman/Sakkit booklet. It costs about 20 bucks and will get you thinking through the issues better than anything else out there. He has a strong concept I don't think he is any more right than another experienced person, but at the very least you will end up being able to analyze the choice from some big picture elements and then take that through to every single detail on the bike.
The reality is the experts can't really save you. Unless you aren't very picky about your gear, a custom purchase ends up being exactly the same as an off the rack purchase unless you know what you want. I would buy an LHT or Gordon cheapo. Do some riding, and then make a decision about a bike when you know everything you need to know about every single aspect of the project. And you are just totally full of opinions about what you want. Then I would relegate that 400 dollar frame to the commuting role and keep the 4000 dollar frame
for the touring ap.
Fit is incredibly important, and it isn't something I want to leave up to anyone else. Either you have a position that makes sense and you can ride all day, all month in or you don't. If you do, what do you need someone else for? I have one shattered leg, nobody can fit me on that, but I fit myself, it wasn't difficult, read a few things, then go out there on a reasonable size bike, and make small individual adjustments until it is super comfortable. Read a bunch of stuff on fitting online so at least you know what the idea is.