Fastest train from Denville to NY Penn is 70 min, fastest from Morris Plains to NY Penn is 60 min, and those are during peak hours (higher rates). Off peak will take longer (more stops). Parking at train stations may be a challenge, so if you can walk it's better. Here's the site for NJ Transit to check schedules (under Schedules & Fares, select Train): http://www.njtransit.com.
You can pick up Lakeland Bus at Bloomfield Ave Park & Ride, which has a pretty large commuter parking lot: http://www.lakelandbus.com.
You can drive via Route 80-280-95 to Lincoln Tunnel, which can be 35 min if you're off rush hour, then you have to park and Columbia U area can be a hassle to find a spot unless you have designated parking. Personally, I'd choose NJ Transit midtown direct route so you can at least read during commute. You'll get used to the best times to catch train on both ends and you can buy passes at commuter rates - same with subway. Good luck!