Yes, small, superficial cracks are normal as homes settle. Older homes have a higher chance of showing signs of settling through hairline cracks from temperature changes, moisture changes, and soil shifting. However, larger cracks, or discolored cracks from water damage, may signify a bigger problem that requires reparations and preventative measures.

Depending on how much adhesive was used as well as the strength of the adhesive, you may have some drywall damage when removing a mirror. You can typically repair most drywall damage if it’s small by sanding the damaged area, applying spackle to smooth the damaged section so it’s flush with the rest of the wall, and repainting the area.

When sanding drywall mud, you’re going to create a very fine dust that may contain silica. Silica dust contains crystalline silica, which can cause long-term illnesses for people who inhale it in significant quantities. Wear a mask while sanding drywall. Then dampen a drywall sponge to wipe the dust off the drywall, helping to reduce the amount of dust that may become airborne.

If you plan on heating your garage, you must install a vapor barrier when drywalling the garage. A vapor barrier protects your garage from frost and mold that can occur through condensation. If your garage is unheated, you don't need to install a vapor barrier. The only exception is if you regularly crank the heat in your car before getting in it. In this case, you may still want to install a vapor barrier, as your car can heat your garage.