[Now, about the gearing.....how low can I get them? And is it feasible to modify a road bike with a lot of mountain bike
Components?]

I have a steel road bike (a Bob Jackson) with a triple up front and an 11-32 cassette on the back. Definitely makes getting up hills easier. But even when I had a more traditional 11-28 cassette on the back, the way I eventually learned to get up hills without having to stop for breath was to go slow. I mean really slow, down to 3.0 miles an hour if need be. That put an end to my HR getting out of control. I do sometimes still have to stop to let my legs stop trembling, so that is why I am adding weight training to my workouts this winter.