@Hclegg from your post it sounds like you waited till the fall sometime on October to advertise the house for rental ( prepping during fall semester start ). Thus the days available for rent is really the start of when you put the house for rent ( i.e. publicly put the house on rent, and actively seeking a renter )-- only you can stipulate when. That is the start of your rental period. So say you advertised on Oct 10th. - by word of mouth or print or whatever, and your renter actually stared from Nov 1st then for 2020 tax year your rental year started from Oct.10th and rental income starts from Nov 1st. The reasons you need these dates is (a) for satisfying the personal use vs. rental use to determine the status of the property income vs. 2nd home and (b) start and determination of depreciation of rental asset.
Expenses that are allowed to be deducted against gross rental income are shown on Schedule-E ( just download and take a look at both the form and instructions for the form ) but generally it is all the expenses necessary /usual associated with maintaining and owning the property such as property taxes, mortgage interest, property insurance, repairs, legal expenses, HOA dues etc. etc. Improvements that increase the value of the property are part of the depreciation schedule.
Pub 527 from www.irs.gov is a very useful publication that goes into much more detail on this.
pk
