There is no effect on depreciation for income tax purposes. Interest is deductible as an expense.
As long as leverage is positive, it generally makes sense to keep the mortgage. If leverage is negative, sell the property, refinance to a more favorable interest rate, or pay the mortgage off. If the free and clear cap rate, using realistic expenses (usually around 50 percent of gross income) is not acceptable, sell the property.
Cash reserves are critical because of vacancy, repairs, and capital improvements that can come up suddenly. A/C units and roofs are good examples.
Acquisitions must make sense and you must be able to sustain your reserves when you acquire them. Right now, in my markets, nothing makes sense.