If you can't get the answers you seek, either from the tube maker, or the bike builder, I'd look elsewhere. 7/4/7 is some pretty lightweight (thinwall) stuff. I'm not aware of any manufacturers producing these tubes who don't specify how it should be used, whether it needs post weld heat treat etc. Then you have butt lengths- different for lugged vs. fillet. Really, if the outfit you're considering to build the frame can't answer the questions, look elsewhere.

You like the geo?, and the tube sizes? Any custom builder can provide what you prefer- but he may have suggestions to the contrary based on his opinions to your personal needs.