The horse I'm getting has Heaves?

It really depends on how bad her heaves are. Get her checked out by a vet before you buy her, and they will be able to answer the last three questions. To help with her heaves, try to keep her boarded outside, preferably on pasture. Sprinkle her hay with water to reduce dust. If she is inside, sprinkle her bedding with water, and strip and power wash her stall about once a month.