I recently took a course on how to properly estimate cost of repairs and rehabbing houses for profit, so i feel somewhat comfortable enough to do my first flip.

Remember there are variable expenses such as vacancy rates, repair rates and management fees so when someone tells you an ROI make sure your comparing apples to apples meaning create a formula you're comfortable with and then run all of your prospective properties through your equation.

He doesn't seemed concerned about having the money secured; however, I just want to make him feel as comfortable as possible and dot all my i's and cross all my t's.  

That way you can give a copy of that to the seller with your offer to make them feel comfortable with you.  

Go with what you and your family are comfortable with.

I plan on doing the BRRRR method and I know that doesn't reach the 30% threshold, but I am comfortable with it. 

I suppose in the long run it will be an asset since you can target the most promising markets instead of sticking to what you are comfortable with.

Sometimes this can be avoided if a title company can get Comfortable insuring the property without going through the whole process.

Put him touch with your lender, so he is comfortable with the situation....availability of rehab money, scheduled draws, draw requirements, etc. 

That's why I am having trouble coming up with questions..Just need questions that will make the seller feel comfortable and willing to trust us with their property.