Addressing your last two questions, it is not correct to include the cost of land in basis for depreciation. Conventional thought is that land doesn't lose its value only 'improvements' built upon it degrade over time. You have taken a larger depreciation expense than you should have in years past. You will have a larger depreciation recapture amount when you resell these assets because of this.
MACRS has 3 methods of depreciation:, 200DB, 150DB, and SL (Straight Line). The use of MACRS by itself is often used when referring to the 200DB method as it is the most commonly used.
