If you want to hills, I recommend Green Pond Road between Rt 80 and Rt 23. That stretch is about 10 miles long. I used to work on Green Pond Road near Rt. 80, and would bike to work from Stockholm, NJ, so I'm familiar with biking on there.
Probably the biggest hills you'll find in Rockaway, and relatively safe to bike on. The only problem is there are some sections where the shoulder almost non-existent, and there's a high curb and a guardrail, all at the same time. It's a good test of balance and control to stay as far right as possible without hitting your pedal on the curb or guardrail. Fortunately, this isn't much of the length. No traffic lights, and very few intersections, so you can ride w/o stopping for 10 miles.
This would be an out-and-back. You might be able to put a loop on end in West Milford (Route 23 has w i d e shoulders there and is very bike-friendly), but I can't think of any good ways to loop back on the Rt. 80 side. You could do Green Pond -> Rt 23 N -> Oak Ridge Road/Berkshire Valley Road -> Something else, but iding on 15 south of Berkshire Valley Road isn't very bike friendly, so things get complicated after that. Even if you continued on Berkshire Valley Road to Rt 46 or Rt. 10, I still can't think of an easy way back to Green Pond Road that's very enjoyable by bike. There could be something - I don't know all the local roads that well - just the highways and county roads.