justcrankn

This sounds like a great adventure.

1. Is the frame whippy? Will it be able to develop oscillations under certain conditions? This is something you wouldn't worry about on most singles.

2. How are you carrying gear? Rack, panniers, bag over the top tube, etc? What will the front/rear weight distribution be?

3. Is the rear brake up to the job? That's your first line of defense if the engine goes nuts. Are parts readily available? I'm assuming the engine won't provide any engine braking.

The concept of using the longer wheelbase for this setup makes a lot of sense, as long as the weight is reasonably balanced. I wonder about the durability of the wheels and rear hub. 25mph sounds suicidal. Will it have enough power to climb the hills? That would be a huge load to pedal up a mountain.
Be sure to bring your insurance card!!!