http://www.catskillguide.com/hike-6.htm
That will give you a rough guide to the miles and stuff. I've never been a stickler to details.. I hardly ever know how many miles I did in a hike. Usually I'll calculate it if I write a trail report, otherwise, I just guestimate the length and go from there! Probably not the best person to ask for mileages.
I believe from a friend of mine that has done the loop from Woodland Valley up the JB trail to the PE trail back says it's something like 16 miles or so. Can be done in a day. I do not remember if that is taking into the account that there is part of Slide Mountain Road you either have to walk down or you can avoid by using the road that goes through the Winnisook Lake property. It's marked I think on the TC maps as a dotted line and its fairly obvious a road when you see it.
Blueberries at Wittenburg, nice views, feel free to check out the Terrace Mt shelter, it's kind of in a neat area and a good break before it really heads uphill.
Ladder on Slide (fairly new) before the summit on the east face. John Burrough's Plaque that you can't miss before the summit. You'll see the concrete foundation of an old fire tower that used to be on the summit of slide.
Nice DEC campsites between Cornell and Slide and a small stream that is the water source.
And as far as exit 19, route 28 west is the first right off the circle which you never enter. When you exit from I-87, just keep to the right most tollbooth that you can use cause the exit for Rt 28 West is right there.
Take a look at that huge-ass RV store (Camper's World?) and marvel at how much $$$ in RVs that must be. The better view is actually when you return to the NYS Thruway south because the jughandle will bring you with a good view of the RVs...
Be careful of cops on Rt 28w from the NYS Thruway to perhaps after it merges into one lane. I always see lots of cops there, especially around the Ashoken Reservoir area.
I've been to the ADKs, I still love the Catskills.. Nothing wrong with loving both!
[edit ] I just saw your reply... There are three logical trailheads to do Slide, Woodland Valley (off Rt 28 directly near Phoenicia).. Slide Mountain Road (CR47) which is halfway on the PE trail near the switchback (also allows access to Panther and Rocky Ledge as a dayhike)
or Denning Rd.
Doing the whole loop as I said above is strenuous, 16.5 miles, 3 peaks is tough but it is doable if you both are fit and get an early start.. Preferrably earlier than 9:30
I think a much nicer hike to Slide if you only want to do Slide and not do Cornell and Wittenburg would be to start at Denning and go up the PE to the Curtis Ormsby to the John Burroughs trail to Slide. Shawn (Snowshoe) and I did this in the winter and it is awesome. It is less of a road walk as the trail from Slide Mountain Road is and the C-O is a very nice through the dense evergreen forest. Don't miss the little stone memorial of Rev. Bill Curtis and Allen Ormsby at the junction of the P-E and the Curtis-Ormsby trail. For an interesting read, you can also pick up "Now Without Peril" which is about Mt Washington but both Curtis and Ormsby both died on. Their story of their deaths was written up in that book by Nicholas Howe
Jay