Gypsum boar should not be exposed to temperatures above 125 degrees for long periods of time.
This product can be used on ceilings in a garage if there is an attic above. If the space above is habitable, then 5/8" Type X gypsum board is required on the ceiling.
10/30/19 Between $11 - $15 per 4' x 8' sheet, plus some change for Gypsum Board. The price varies based on which specific board you select. This is the current price; prices may be subject to change. Recommended is that you go on line or simply visit a local Home Depot to determine exactly which you want, learn the exact price. Some construction items also come with a volume discount, so if you were going to buy a LOT, you might want to ask about that, see if it applies.
I would think it would fine if you use a mildew resistance primer and paint. I have it in my house in the snow level with no problems
Description says "45.6lbs".
Gypsum board is water or moisture resistant.
No, never! You don’t want anything heavy above you. Suspended ceilings are not made for that kind of weight. Imagine an earthquake with that falling down on you. Acoustical tile would be the best option.
Drywall should be attached with screws that go at least 5/8" into the wood, so for 1/2" drywall use 1 1/4" screws or longer.