while prices have dropped considerably here the market is just approaching the point where income will cover expenses (with minimal down and including all associated costs) I am a Broker Associate and own 4 area homes 2 of which are in the 08540 zip code. Be careful as this is merely the route the postal carrier takes and does not indicate an actual township. The notion of town home or condo investment may be best for you in that it may limit your exposure as far as conditions of unit. (roof, or other structural areas are often not individual owner responsability). Personally though I wouldnt limit my self to these and would opt for a good inspection to know condition and risk. As I indicated that 08540 zip includes Princeton but also parts of Franklin Twp, Lawrence and others where prices are much less.
Suggest you meet with a few agents, ask for references, ask what properties they maintain and if they have investment properties of their own. Those who can, do.