disclosure: I'm no expert @Ethan Perkins
I don't think you're being cautions enough with your vacancy, repairs or Cap Ex #'s. 5% on vacancy and 7% each on Repairs and CapEx are likely more realistic. You don't have any insurance or utilities or other expenses factored in either. I'd also factor in 10% for Property Management. Even if you plan to do it yourself now, plan for it so you can see what this property will do down the road when you need it.
If you rerun the #'s adding all those in I don't think this looks like near as good of a deal.
Also are you planning to do some type of HM or PM loan on the front end? Not sure how many lenders will do the full value of purchase price, even if you are putting in your own part for the rehab.
Also make sure that you actually have a lender that will do the Refi after just 4 months. You'll likely have to have your rehab done before you can start the refi process and I'm sure it will take 30 days for it to actually get done.