Howdy @Christopher Berggren
I realize this is a little late. Here are some responses and comments.
1. The most important numbers/ratios I look for in analyzing BRRRR deals are these; ARV, All-in Cost compared to Refinance LTV, Income/Expense ratio, Cash Flow using 50%, and COCROI after Refinancing.
2. The two ARV's are different because the first is a number you entered ($585,000). It should be based on comps. The second is derived from the calculator using the stated NOI ($38,121) dividend by the Purchase Cap Rate (rounded to 9%) which gives you a Cap Rate based value ($423,566.67).
3. Regarding your Refinance loan amount. How did you arrive at $461,500? Most lenders use a Loan to Value (LTV) metric to determine the maximum loan amount. A 4 unit property is still considered eligible for a Residential loan. However, it is also considered an investment property and therefore normally only qualify for 70 - 75% LTV. 75% is $438,740. 80% is $468,000. Double check your financing before you actually purchase a property.
4. Your Purchase Closing costs seem low. @Brent Coombs covered the Acquisition Loan issues.
5. Your overall Cash Flow analysis is a little too optimistic for me. 38% is not very conservative to start with.
6. The last thing I would note is your suggestion to add a 5th unit. This changes the description of the property from Residential to Commercial. You would need to check with zoning to see if it is allowed. Any future financing (i.e. your Refinance loan) would now be a Commercial loan with different terms for amortization, Interest rates, and shorter loan length with balloon payments. Again, double check your financing.