In order to calculate your debt service ratios, some more information would be required. If you purchased a townhouse for your residence, did you qualify based on your income? If so, and as long as your other debts have remained relatively the same, you should be okay.
You may not be considering that the banks will use the rental income from a rental property to offset the mortgage payments. Every bank will use some percentage of the rental income to your credit. If you are buying properties with good cash flow, then as long as your personal expenses are in line with your income, then you should not have a problem.