Aircraft booking:
2 Options - either draw lots at the start of the year and then you rotate the weeks accordingly (with maybe 2 weeks in summer), OR
Internet Booking - first come first served (within reason - say you can't book more than 3 months in advance or similar).
http://www.aircraftbooking.co.uk is a very good aircraft / licensing management system for not a vast amount of money annually.
Agreement - Sample of a generic one on the AOPA website, or some kind soul here may let you plagiarise theirs (I'm sure I've got one at home if you want to drop me your e-mail address).