Palak,Many online tools like RentSavvy, Avail, Turbotenant, RentRedi, Apartment.com help you do this process. 

These properties cover my mortgage, allow me to save for maintenance/repairs, and are projected to be worth $7–9 million by retirement.

 try one of those online sources like prosper etc. 

The promise of accelerated depreciation and immediate tax savings is attractive.

Saving 15% for repairs/vacancies/capx. 

If I do 1031 exchange can I  save on  taxes ?

The increased cash flow would make such a substantial difference in your daily life that not paying it off would be foolish.Outside of that, I can't see many reasons I would take a 15% tax hit to save 4% on a mortgage, which is really only effectively about 3-3.5% depending on your tax bracket.

The current tenants are month to month and not interested in buying, and the existing mortgage balance is assumable (3.65%) for qualified buyers.I know it's a great house -- and with the assumable mortgage -- a great buy for someone looking to save with current interest rates sitting as they are. 

Also just look online and steal some ideas...I used to Google Luxury Kitchens and then figure out how to do the same for less $$.You'll be fine with your experience.

Tenants save money when using a shared meter, so there's plenty of room for error when calculating how to distribute the charges.