Have you asked him to finance the property for you so that you can get someone in the 4th property and do any repairs needed? If your current goal is to refi in 6 months you would pay financing fees and closing cost now just to turn around and pay financing fees now. Pitch to him that you would take care of the management and worries and all he would do is collect 1 check for all the property directly from you. This would give you time to shop around for the next few months while collecting rents from the tenants. If he is an investor he would be more open to this then a traditional home seller, especially if he has no loan or would allow you to take the loan subject 2.
For your list, is this in the correct order you plan to do things or just a list as these things came to you? If in the order you plan to work your plan I would personally put the home under contract pending inspections so that you are not spending money on a deal that may get swept out from under you, this is the reason you have a due diligence period built into your contract. I have renegotiated deals after the inspection if you find out there are major issues with the home. Offer a low earnest money or due diligence fee until inspections are over then bump that up if he requires more down.
Current leases are a must have when doing your due diligence, and I would talk with each tenant to see if they would be willing to sign a new lease and application so that you can view the most recent information on them, some of the worst issues I have had has been taking over problem tenants, I would almost rather homes be vacant so that I can screen and fill as I see fit. Maintenance records and profit and loss statements would go a long way for your lender package as well as your peace of mind when formulating your numbers.