Sandy beach. Ok sized on low tide, almost no beach on high tides. Then the beach becomes dangerous for kitesurfers, since you will launch kites next to rocks.
Winter is very cold. Wetsuit needed in spring and autumn. Summer can be without. Bayside: winter temperatures usually about 38°F, summer 75°F. Ocean: winter temperatures usually 38-45°F, summer 68-72°F.
From New York City, take New Jersey Turnpike south to Garden State Parkway (exit 11). Take GS Parkway south to exit 117. Take Route 36 east for ten miles. Cross bridge and stay on right lane for Sandy Hook. Ferry service from Manhattan to Highlands, NJ, is another option, then take cab to Sandy Hook. Car trip is 1 hr and ten minutes from Holland Tunnel, Jersey side. Summer charge of $10 per vehicle. Small parking lot.