If you intend to purchase a less expensive home than the one you intend to sell, chances are the down market will work against you. If you buy a more expensive home, with income producing potential, the market could work in your favor.
As others have said, being a landlord is another proposition and requires investigation into the rules, laws and processes involved. Will you manage it yourself or pay for property management? Will you be able to handle extended vacancies, repairs, maintenance etc? In a perfect scenario you have a great unit, easy tenant and the money flows in. Whether you can find the perfect scenario is another question.
Talk to people you know who are landlords and discuss what you are considering. Discuss income producing properties with a local agent with experience dealing with them. Talk to your accountant regarding tax benefits/consequences and make certain you know landlord tenant law in PA.