could you set it up as an escrow item(credit from seller) and use a written estimate for the after close repair escrow?

If he funds the purchase and repairs, I will do all the work (meaning some demo, finding/scheduling/managing contractors & projects, etc) we will spit the proceeds.

Properties are older ranging from $20K-$50K and needing about $30K-$50K in repairs.

I don't want to drop lots of money to litigate something that may only cost a few thousand to repair, but on the other hand, if it's reasonable to request the previous owner to pay for this, I would like to do so.

It's just standard operating procedure. 

And I don't start showing it until the current tenant has fully moved out, and I've had a chance to make any necessary repairs and have the place professionally cleaned for the next tenant. 

There are many good home flippers, but more times than not, flippers cut corners on repairs in order to make the most money.

I had figured the following expenses: vacancy/credit (8%), Property Management (8%), Property Taxes (4%), Insurance (3%), CapEx (10%), and Repairs (5%).

In order to know if the property you are considering is a good deal, you will need to know the neighborhood, the comps, the amount of repairs needed and their costs, the amount you can rent it for, the financing you have available, etc.

The owner is currently in the process of updating and repairing the home herself.