Does one have to clime up down lots of stairs to get in / out of planes or is there a bridge from planes to terminal

No not at all. Very easy to manage

The access to the hangar is via a bridge. There is a small elevator at the end. To get INTO the planes, there are stairs and some small elevators. I've never used them, so I can't give you more details, other than they are small. And I'm not sure if they are on every plane, but one would think so.

The access is via jet way. No stairs. Can't confirm you won't have stairs at the connecting location.