The Svitak 2015 100 mile route on ridewithgps. It looks like the 100 follows the 67 route, then adds an extra loop instead of stopping at the finish line. (It looks like the northbound last segment of this 67 is different than the 2015 map.) So you should have plenty of sag stops along the way.

Yeah, that looks great for a first time century ride. The steepest grade is 4% (but ridewithgps can be wrong sometimes on very short, steep climbs). Even the "big climb" around mile 50 is 230 feet at mostly 2% to 3%. That steep looking climb at mile 96: just 110 feet at 2% to 3%, easy. The total 3000 feet for 100 miles is an easy "flat to rolling" ride.

It could be windy, I suppose. And maybe hot -- I'd fill two bottles even with lots of rest stops. I'll splash some water on my arms and legs if it's really hot.

You don't really need to ride an 85 miler first. A local hilly 85 mile ride would probably be harder than this 100!It would be helpful to do a 6 to 7 hour moving time ride (basically ignoring the mileage) before the 100 mile ride, to sort out any long ride problems.

~~~~
On my few 100 mile rides: I've looked at my bike computer after riding for quite a while, and it would show "18 miles" or "22 miles". Woah, I've got 80 more to go! Intimidating! But once I get to 40 miles or so, it starts seeming quite doable. Finally, counting down the last 5 or 8 miles seems to go on a long time -- I try not to check the mileage excessively!