Make sure you don't add too much too soon. 80-90 miles on the first saturday, even at a slow pace, could increase your chance of injury. The first week start with maybe a 20-25 mile ride and add no more than 10% every week. This will have you hitting 100 miles way before March and it will give you plenty of time to adapt to spending that much time in the saddle.

Make sure you have lots to drink. On a hot day, try to drink one bottle an hour. This could mean stopping along the way to buy water or stuffing extra bottles in your jersey. Also, make sure you pack food. Cookies, sandwiches, whatever you want.