So glad you've already plugged into the Bigger Pockets podcast - that was a huge source of education for me when I first started.If you haven't already, I would recommend finding a real estate agent that you trust (you've already had a few chime in here with recommendations ;), and also start talking to lenders (banks, mortgage brokers, credit unions, etc.)

You can pull out a HELOC (Home Equity Line Of Credit) Or a Home equity loan on your SFH, and use that money towards a downpayment.

If you go the HELOC route at any of these credit unions, you should be able to get the $24-$48K you are looking for. 

Sounds like you're on the right track towards your financial freedom.

The terms you can expect will vary based on your experience, reserves, and credit scores and of course the property details.   

With one property I would not bother with a separate account, but keep good track of your expenses using software to categorize.

With good credit and a low DTI, youd probably get about a 4.75% or so right now.

Are you in charge of background checks- do you credit and criminal, other states> do you verify, etc.What happens in a hurricane when they can't go in the house for 2 weeks?

One column I use is "Projected Costs", another is "Actual Costs", and yet another is "Paid", which keeps track of whether I've paid the bill or not. 

Can I report to a credit agency in MA?