@Luke M.
I haven't checked out the rental calculator yet, but the more I'm thinking about this, the more I'm questioning that extra 10% for capital expenditures. I mean, if this is meant to capture the accounting expense for depreciating capex costs over time, then it should be treated like Depreciation on the structure, no? Not with respect to depreciating it over 27.5 years, but meaning, it wouldn't be considered for calculating cash flow.
Depreciation, capex and adding back principal pay down would be considered after cash flow, only for calculating taxable net income...I think.
Bottom line, unless you think you'll actually have out of pocket costs at $1,800 per year (20% of rent), on average, for repairs of all types (IRS "repairs" and capex) then you might consider lowering the total of repairs/capex to something below 20%. For some perspective, that seems like enough money to buy appliances and a hot water heater every year, or replace the roof every 4 years...again, I think.
It just doesn't sound right to me. I hope some seasoned landlords will weigh in on this, as well, so we both can learn. :-)