What an interesting thread. You asked for advice and you got a bundle. It's interesting how many people want to talk you out of a custom frame, and the reasoning behind it. I agree that it is a risk because you really can't test ride one before deciding. I have 7 bikes, two are custom, and they are the two bikes I ride the most. They are comfortable, they handle well, and do what I ask of them. Both were a risk, but well worth it.
I too have been building a dream touring bike, but it isn't a custom. It's an 80's Specialized Expedition. Only money issues have kept me from finishing the build and off the road. To each his own. Listen to the advice, then do what makes you happy. You deserve it. Then enjoy your tour. Even if you only do one tour on it, it will have been worth it because you will have achieved your dream.