Glad you're interested in Carleton! I graduated a few years ago and had a great experience both academically and athletically. Mileage is largely determined by what you've done before and what you can handle, with the general guideline of increasing by 10miles/week/year. Workouts range anywhere from 4-8 total miles of quality running, mostly aerobic or anaerobic threshold type stuff during XC and 1500-5k pace stuff during track. When I was at Carleton, the team was very supportive and consisted of a bunch of guys looking to have a good time and get the most out of themselves athletically. The current runners tell me the same is true now.
I'd suggest that you email the coach, Dave Ricks, and talk to him. Overnight visits are highly encouraged.