I didn't mean to discourage you at all; since you asked, I though I'd offer some information. I've ridden that route a number of times, and riding through the park can be pleasant, if hilly, and crossing the Henry Hudson Bridge on the walkway is easy and low stress, once you find it. I'm not familiar with the Broadway Bridge, but by reputation, it's a mess of traffic, and rather unpleasant.

The stairs over the train tracks are about as onerous as any long flight of stairs. I carry my bike without too much trouble, but with bag, it's maybe thirty pounds, rather than 70. There's also a short flight of long, shallow steps as you come off the footbridge. I'm not sure if that counts as onerous. Entering the park from 218th St. saves you the trouble of climbing the stairs, but you ride up and down a hill instead.

Noglider, when did the switchback open? These days, when I go up to Inwood (about once a week), I take the streets, and the path along the Harlem River.