Usually added units above what is allowed is a hard no.

If using Realtor(c) forms, don't hesitate to fill an entire blank Addendum page of added language to protect yourself.  

I know the opportunity cost is significant, there are many things we could do with that extra 1,500 over the course of 10 years (180K).

Make 15% & enjoy the $15k per year in extra income!

Most PMs don't deal in LOs so they wouldn't be able to help there either.If you're not in a rush then your best bet is to monitor kijiji and call/text/email every For Sale by Owner ad with a house that matches your criteria and ask if they would consider doing a rent to own.

Do you have an extra bedroom you can rent out?

If you are adding central air that has to be figured into your price. 

That added risk means they'll pay less.Pursuing tenants who have vacated is usually break even at best. 

An appraiser is obviously going to inspect the house and our concern is that we then would not be able to finance as a duplex, not to mention the added property taxes.Listening to Brandon Turner's The Book on Investing in Real Estate with No and Low Money Down, we thought maybe this property would be a perfect candidate for seller financing?

I am about to start a new rehab project and was thinking about adding some sort of security system in it to monitor who is coming in and out of the house and overall security.