Is it best to put in the values for mortgage interest, taxes, insurance, etc exactly as they appear on the tax form and let Turbotax calculate it, or should I do the math myself based on days in service and enter separately for Primary residence and Rental on that same property.
Yes, you should do the math for this first year based on days of rental use against the days in the rest of the tax year. Calculate the percentage of mortgage interest, taxes, insurance and enter the rental portion in the rental activity. Enter the balance as itemized deductions for mortgage interest and taxes.
In the rental activity you should select 'it was rented all year' and that it was rented at fair rental value (FRV) if you are renting it at that rate or close to it. Prorate any and all expenses that would be for both the rental activity and the home.
When you enter the home as an asset, you will enter the date of purchase and the date you placed it in service for rental. The date placed in service will be used to calculate the depreciation. It's important to select Residential Rental Property. The amount allowed is the lower of actual cost or fair market value (FMV) on the date of conversion. Usually this is the cost due to appreciation in value in most area.
TurboTax will calculate the correct depreciation on the cost less land.