will start over at 27.5 years?
Absolutely. It's starts over with the new adjusted cost basis with 2020 being year 1 of the next 27.5 years.
Also will the acquired/purchase date for this "new" property start on the day you make the conversion?
The acquisition date and the conversion date are two completely separate things. Your acquisition/purchase date will never change for any reason. Not ever. The date you convert it from personal use back to a rental will be the date in 2020 that is the first day a rental "could" have moved in. Depreciation starts on the date of conversion, and has nothing to do with the date of purchase/acquisition.
