1) Whatever students need. To help them with their ideas, and to help them understand by letting them experience the fails and successes when it comes to design, organization, structure, etc. Many times 'advising" certain things when it comes to fundraising or when there are limited resources is necessary.
2) By either less days with more productivity or by more days with less time. Let mentors delegate at times what their subsystem needs to accomplish and have students come up with designs by the next visit. It works. If they need help, they have a phone number or other mentors who are present that day.
3) A list serv works best for . Robonauts and Pearce Robotics use to rely on email but I am currently converting the latter to a listserv mailing list that has one for mentors, one for students, and one for all members. We have others in the works (parents, sponsors, etc) for different blasts but these are the primary. This system should be live in a matter of weeks.
Link to listerv:
http://www.gnu.org/software/mailman/
You can use Google groups but I like the notion of many listservs for different things and I like to be in control of my own data, therefore we decided to use our own.
For anything regarding the above just message me or email me and I'll do my best to help you out.
Pavan Davé