We do a few of these things, although use eDirectory and Zenworks rather than Active directory/SMS.
Some of these things are fairly easy:
Which machines are being used - entry in login script that writes login id, computer name, login date/time to a database running on a server on your network (SQL express or MySQL will be good enough for this, but if you have a decent sql server box with extra capacity feel free to use this).
Over time this will give you details of how much is used over time (you could also analyse the windows event logs on the workstations for logon / logoff events as well).
If your workstation naming convention includes a lab identifier then you can group on this in your reports; if not you will need a table linking computer names to room names. Your reporting for your lab techs can take data from these tables, so it is live.
Be sure when writing your reports to exclude any scheduled classes taking place in those rooms.
Regarding maintenance - can I suggest a routine schedule of maintenance that encompasses everything you are likely to need. During that time - and this varies each month - anything from workstation reimaging and patching, server patching and reboots, DNS reconfiguration, switch recabling etc is done.
This is published well in advance to allow people to work around it, including details of who (in terms of buildings, departments, corridors etc, applications / services) will be affected.
Normally ours is 6:00 - 9:00pm on the first Wednesday of the month, but occasionally it is changed (eg if that week has lots of student coursework submission dates).
Depending on what is done, the relevant IT staff work late but get time off in lieu sometime over the next couple of weeks or so - so you don't want everybody involved so people are available the following day - but be sure that those in leave notes over what happened and anything to take account of.
For anything that's too big to do overnight its typically done over a weekend.
Regarding student numbers, if you have an IT helpdesk office, when students come in asking for help, ask them about it - possibly have a general student survey.