This is a mtn bike ride. Off road distances on the Roaring Brook Trail currently are approximate.
If you are a gifted cyclocross rider you can possibly do this route, but short of a real challenge, you want to use a suspended mtn bike. You will walk sections and there are real obstacles on this route: rocks, roots stones, streams, mud puddles, downed trees, holes, ticks in season, thorns, possibly poison ivy, etc. You need to know your limits. Body armor might be in order but will not be a guarantee of emerging injury-free. All sections of this route offroad are multiuse trails so you have every right to use them. If you understand the risks and effort, the rewards can be great. This is not 9w to Nyack. You will be in deep woods with boulder strewn hillsides, along deep gorges with sylvan streams, moss covered ledges and occasional views.
Don't let the distance fool you as to your average speed. This is a vertical route. Between grades, walking your bike up and down crossing streams and puddles you might spend 6 hours from station to station, perhaps more with mechanicals or less skills.
Tell the folks at Niese's that you are from the NYCC and that the old bearded biker sent you. BTW, the ancient auto chasis to the right on the Stillwater Trail (yes, this was once a passable road) was the owner's uncle or grand father's, something like that.
Should you be overwhelmed or short for time after emerging from Sunken Mine Rd, continue straight from North Shore Rd onto Oscawana Lake Rd/Rt 20, a left down Tinker and a right on Peekskill Hollow Rd and follow it to Peekskill. The next exit afterwards is a right on Wiccopee Rd (rather than the left to Niese's) and then a right on Peekskill Hollow Rd. Later, when you emerge onto 301 off the Stillwater Trail, just follow it down all the way to Cold Spring.
The Moneyhole Mtn Trail is now on the WRGPS file, however the Roaring Brook Trail is not. Photo of Moneyhole Mtn Access from S Highland is on link above. Although this is the route, it is actually the access to the trail, marked in green. You will join the trail itself, marked in yellow, as you bear right further up. The optional trail to the viewpoint on Chimney Hill has white trail markers, click on link for photo of trail's start. This side trail will add 100 vertical feet to your ride, but it is challenging, interesting and a good place for a rest stop. It comes off the Moneyhole Mtn Trail, to the right, as you enter a large pine forest, just after cresting an ascent. In clear weather you can see the Great Gap in the Hudson Highlands and Perkins Tower on Bear Mtn.
The Roaring Brook Trail, picked up off Wiccopee Rd is less than apparent. Wiccopee ends in an unpaved parking area. The trail starts at the far end, on the right corner, from where you enter the lot. There will be a sign, but you will probably have to look for it. The access trail begins with a steep downhill crude path from the parking lot. Follow the path to the left, north. Within 0.1 miles you will encounter some standing muddy ruts gouged by ATVs. Walk your bike around them, not all that easy to do without stepping directly in the mud. The trail will be within earshot of the Taconic Parkway for what I would estimate at least a half mile. It will then climb a steep grade and then descend to the right of one of the nicest spots in our region. Boulders and fallen trees cover a hillside with a ravine separating it from the path. Further up there will be a couple of stream crossing where you will need to get off your bike as they are not all that friendly to cycle over. Once you can see Stillwater Pond on the right the trail will be entirely rideable.
On encountering fallen trees blocking your path, look for impromptu side paths to go around the log, or get off and haul bike and self over the obstacle.
In additon to your standard emergency items you carry on road bike rides, ideally carry a spare derailleur hanger (universal, or specific for your model bike), a master link for your type of chain, a multi-tool for knocking out chain links, and a map of your route. A space blanket in your pack could make the difference should things go from bad to worse.
Be mindful of hazards on the trail, but have fun.