If I have said it once, I have said it a thousand times. Of all the bikes I own or have owned, including the custom frame I have, there is one bike I would keep if everything else had to go. It is a 1984 Miyata Ridge Runner. I have it configured as a cruiser and run errands of 10 miles or less, and ride the neighborhood each night with the Mrs. The bike can do anything with the correct change in parts.
Going with a custom frame is always a great idea as nothing fits like a custom. Mine is 22 years old and has served as a road burner, long distance commuter, loaded tourer, and general all-round bike, but not quite as configurable as that old Miyata. One thing I recommend is looking at old touring images from the 50-70's, specifically european images. You will find "tourist" handlebars commonplace. Simply put, a standard touring bike with tourist bars so that the rider can sit upright.