Hi Steve,
As with Sean's comments/advice...I think you are thinking through this brilliantly. Being and engineer yourself and still willing/wanting to have a PE still stamp your frame speaks volumes to your level of dedication to detail.
It also appears you have done a great deal of reading and research. As a teacher and Timberwright I am keen to point out to most folks without a background in design, art or architecture, that they may "think" they can design...but often can't. With that said, you have followed the "wise path" of actually following the "vernacular." I personally take little credit for my work as it is usually a "team effort" and so deeply vernacular in nature as to be hubris to believe I did to much than "replicated" and make a few adjustments. You have chosen a "salt box" and that is as vernacular (and beautifully simplistic) as they come...Hard to go wrong there or fault.
1. If I have a fairly detailed Sketchup model of the frame, can I approach a pro and ask for an RFP (as was described in the designer thread) to get a general sense of what the frame might cost?
Yes...
Anyone actually doing this for any length of time at all will have no issue giving you a fixed price for your frame in a metric of square metre (or feet), or board foot. Both standards for a very long time...
You can expect to pay no less than $25/ft2 and should not see anything higher than $50/ft2 depending on region, wood species and Timberwright's experience.
2. Will a Timber Framer want to redraw my design in their own program as part of the design process?
Most (all???) shops today of any note are more than comfortable with Sketchup...that really should not be an issue at all. Small adjustments here and there, but with such a design as you have described, I would not normally anticipate much of an issue at all...
Good luck and keep us up to speed with your thought process and progress...I (we?) learn as much from these exchanges as you do..
