Since the property will not be available for rent or actually rented in 2020 then you will not enter anything about the rental on the 2020 return since it is not a rental property yet.
On the 2021 return they cost basis of the return will be used for depreciation purposes. Cost basis = purchase price + cost to buy + improvements/repairs.
I think you need to educate yourself on what the IRS expects form a landlord on a Sch E : https://www.irs.gov/forms-pubs/about-publication-527
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