For rental property purchase, consider the location, purchase price, population density, percentage population increase, job employment data, and cash flow. Prior to purchase, place a few contingencies in the purchase contract for home inspection, financing, appraisal, title with a placeholder of Earnest money.
FinTech bookkeeping app, use Baselane.com
http://www.rentometer.com/ helps estimating the rental income.
https://www.propstream.com/ provides info on the property's owner, mortgage and taxes owed etc.
https://www.notion.com/ can help keep track of multiple properties with a dashboard outlook.
For maintenance issues, contractors can be hired via https://www.thumbtack.com/