Read as much on the subject as you can. 

You definitely should read book on the subject but the best Advice I can give you is to make a appointment with your Accountant and Sit down with him.

Most DSCR lenders will base their loan (Rates and Leverage) off the income of the subject property, verified by a lease agreement.

I've watched most of the Webinars and read many blogs on the subject. 

I realize this is highly subjective with a lot of variance, but there must be some average square footage per living unit that one could baseline 'cramped' units against 'spacious' units in an area.Local building code?

Thats a great subject to deal, not seller financing!!!   

I'd just make my offer subject to being vacant prior to closing.  

@Jimmy Suszynski This is a very specialized subject.

I know how to do comps, estimate rehab costs, and give the seller different ways I can buy their house depending on their situation whether its cash, options, lease options, subject to`s, seller financing etc.So, bottom line, if I can get sellers contacting me, I am very confident that, if their is ANY potential to do a deal I will find it, I just need to implement a system. 

For most effective use of his time have at least the outline of an operating plan in place.