Make sure you are well hydrated and have enough fuel before you go. After a ride strech your quads at least and if it is over an hour take some recovery drink or chocolate milk - it does make a difference.

I like hotter days so Chicagoland suits me fine - 70s are too cool or me. Don't rule those days out, but take it easy and only stop every 1/2 hour or hour. As long as you are moving the air should cool you, but if you stop for too long you will overheat. On cooler days I would just go the distance.

Good luck - it is certainly worth it health-wise and weight-wise on many planes! You can ramp up pretty quick with enough discipline and the right amount of rest between rides. I find if I rest too many days it is tough, so sometimes doing a "recovery" ride taking it easy is better than not cycling as far as recovery goes.