Do you have old doors that I could use as a sliding door?

Yes - you just have to keep checking

Does Habitat restore accept layaway?

Preservation station has many old door that you could use as a sliding door, if you don't find one at the habitat store.

It's hit or miss because a lot, or all, depends on what's been donated. When someone has something to donate, they have it until someone buys it. I just pop in once on a while to see what they have. Maybe they can put your name on a list if what you need comes in. Otherwise try the antique stores on Nolensville road, just outside Davidson County. I always see doors at those places.

They might.