Hey all -
Thanks for your comments! I had the jackshaft idea too, but thought it was a little too complex for this round. Let me put it this way - I might turn out to be a passable fabricator at some point, but a mechanic I ain't. Even the oil on brand new bike chain kinda makes it not my favorite part of the whole process.
My personal wuss issues aside, I went through and rewelded all the joints on the crank. I was able to fill in the 3 or 4 holes that I made the first time around, and basically extended and completed the rest of them.
With the crank brace, rewelded crank, and electric assist, it works like a charm. I took it up and down the street, down the cul-del-sac, and back. I haven't decided yet on the gears or not - for a vehicle with no long distance requirements, it seems like too much. So far, the best strategy seems to be to keep it in the second-lowest gear and use just enough electric assist to keep light pressure on the pedals. Uphill, that's almost full throttle. On the flats, you can stop pedaling and the motor will propel you much faster, but then it starts to feel illegal.
1 brake was enough to get me safely down the hill, so 2 ought to be just fine - I really have a single destination in mind (Simpsonwood), so as long as I take the long, flat way, should be no problem.