You're probably better off doing as much ground work before going to see an engineer. If you do decide to go to an engineer, make sure that they specialize in traditional joinery when building with large timber. You could also look at some of the larger timber framing design/build companies to hire for consulting regarding the design, structural sizing and possibly a reasonably priced engineer.

Either way, to achieve constructing a frame the way you imagine it to be, avoid the professionals with minimal experience regarding your build and you should be able to keep yourself on budget and time.