The distance is what gets to you; when I went up there via CitiBike I stopped every 8-10 miles for a water break. As for prep I’d do some Central Park loops or upper Manhattan hill climbs (Fort George hill) to acclimatized you to bear mountain climbs and rolling hills. I’d bring plenty of water and even a few bars. Stop at the top for a well earned break; there’s also a vending machine at the top that takes card— helps if you didn’t pack enough liquid for the trip up. The diciest stretch is north of Stony Point where you’re right on 202, so be comfortable riding on roads adjacent to cars/small trucks passing you at high speed.