Do not have it put together in the room without knowing it can be moved from the room without taking it apart. Know how it went together and how to take it apart. You will forget so take pictures.
Buy the smallest size you can, one that can be moved by one person.
If you don't have a dedicated work- out room for one don't get one even if it's a free one.
If you don't mind a big upright freezer laying down in a room then you won't mind a big treadmill being there.
I will never have another treadmill in my house.