I can't answer all your questions, but after fiddling around here is what I did to replace the reserver's name with the summary information in the monthly calendar view:
(using version 1.1, but likely similar in 1.2.x):
in the lib/ResCalendar.class.php, change this line:
print_month_reservations($this->reservations, $this->firstDate, array('fname', 'lname'), false);
print_month_reservations($this->reservations, $this->firstDate, array('summary'), false, $is_private);
Hope that brings you one step forward! I imagine the variables to be replaced are similar in the Bookings and other calendars. Cheers.