If your mortgage + taxes + insurance is $1,700 on the rental property, you'll want to generate $2,100+ in rent in order to be theoretically in the black on day 1. That accounts for 1% in upkeep costs as well as a 5% vacancy rate (YMMV). If you decide to have a property manager, you'll want closer to $2,400-2,500.

In my experience, upkeep costs are higher during year 1 when unexpected items often come up. Same goes for vacancy rate, especially if one unit is unoccupied.

Not sure what state/country your in, so talk to a CPA about your situation, but a rental property has an interesting impact on taxes. Here, I take my rental income and subtract mortgage interest, taxes, depreciation (over 28? years I believe), and repairs. That gain or loss is then added to my personal income.

The risk is always that it sits empty or you can't sell it if your financial situation changes. The litmus test for me has always been - am I going to lose this property to the bank if it sits vacant for 1 year? However, that's a personal rule and there are plenty of investors who won't be abiding by that.