@Kyle M.
The effective tax rate will not come into play as much as you think. The primary reason being is that unless you own the property out right you will most likely show a loss for a single property (you will want to consult your CPA). Take a look at Schedule E of the tax return. One of the big benefits of real estate is your ability to take depreciation on the asset. If you are collecting a total of $100/door/month in cash flow (this is after all expenses including debt service) you would have an additional $1,200/year in revenue however, depreciation of the asset may be well over that depending on the value of the home. One example off of foxbusiness: "The tax assessor's estimate of the land value is $75,000, and the building value estimate is $125,000. Your depreciation expense that you take each year againstrental income would be $125,000 divided by the IRS allowed 27.5 years of useful life (residential real estate) for a depreciation expense each year of $4,545."
If you total revenue is 1,200 in pricipal you have a net loss of (4545-1200)= $3345