I don't know where you are I was not able to give you any answers with your geography.Build your buyers list by making good choices when you get good deals. 

Most bank won't lend to you if this ratio is above 43% (there are some types of "debt" that may not count towards this ratio, and some types of "income" that won't count as well, but that's the basic rule).But conceptually: if you or your Dad had sufficient incomes and little existing debt, I think your idea is great--it's what people on BP call "house hacking" (living in one unit and renting out the other).

@Ginger Jones Even more important than the market choice, is the choice of the team you work with. 

but others thats all they want to do... so its all personal choice right ?

In my opinion the lead investor will likely make the right choice but there are some instances where they make a little extra risk and hold on for potential appreciation.

Would 20% down be sufficient? 

If you're that fearful, I doubt any amount of money would be sufficient to thrust you into action.

Either way, you're giving them a choice to earn for sure money now, or spend thousands of dollars on a chance.

We would like to present 3-5 owner-financing choices/alternatives for him to select from.Does anyone have experience coming up with choices that vary along term, interest rate, purchase price, percentage down, etc.?

I want the name to be creative enough to grasp the interest of our future customers, it has to be memorable enough for them to consider is as their first choice when in need of a contracting service the my competitors provide as well.