1) Offset for Main Home only goes back 5 years, so for tax purposes, you had 100% rental use.
2) Land is Always a separate category, not combined with or offsetting building/fixtures for depreciated value.
3) Basic rule for residential houses: If it is attached to the structure, has same depreciation (27.5 years). Not realistic, but the rule.
4) For additional IRS guidance, see https://www.irs.gov/publications/p527 .
