Buying cash flowing properties that do not need a lot of immediate work will allow you to build up a sufficient capital expenditure reserve so that you will have the funds to preserve your investment and to make improvements when it becomes convenient and/or necessary to do so. 

Did you budget for repairs and capital expenditures when you ran the numbers on this property? 

Another 10% should be set aside for capital expenditures (roof, driveway, or other large expenses).

I bought these because I know the area, they were newer properties, they would cash flow, they’d appreciate, and capital expenditures should be low.

This could include taxes, insurance, maintenance, property management, and setting aside money for capital expenditures (roof, furnace, driveway) or vacancies.As a general rule of thumb, about 50% of your income goes towards expenses and/or setting aside to build a reserve fund.

Once it's under contract, get an inspection, figure out what the immediate and amortized capital expenditures look like.

Investors should always have; a down payment, closing costs, money set aside for capital expenditures and a reserve fund.

The main issues I'm reading is:1) Miscalculation of expenditures...

Keep in mind cash flow is what you have left after paying the mortgage, taxes, insurance, and then setting aside/spending about 50% on maintenance, vacancies, capital expenditures, etc.

Since it was not a rental in 2020, am I able to list capital expenditures during the year of 2020 on my taxes when I file in 2021?