no access to hills during winter

Do the stairs have to be continuous? E.g, could I run up a flight of 10m 3x (running back down fast) for the 30m runs? or?

Yep, I found mine on the side of a road then went to home depot and got a rope and chain for a few bucks.

use an eye bolt and 2 big washers.

Henk Kraaijenhof used parking garages for hill substitute. They also did a lot of sprint work inside shopping malls, since there were no indoor tracks at the time. This was done with Nelli Cooman.

When? VERY early in the morning? I know there are walkers in the morning but I never thought about doing speed work in the mall. I would worry about looking odd sprinting in the mall in a post 911 environment.