The cost basis is calculating the purchase price + cost to buy = cost basis
(cost basis - land value ) x the rental portion % = depreciable cost basis for the rental ... you MUST take depreciation so do not skip the asset section in the interview ... and the land value for the rental will be zero. You will divide all common expenses like mortgage interest, taxes, insurance and any shared utilities.
Read up on the Sch E here : https://www.irs.gov/forms-pubs/about-publication-527
