Being responsible for the hardware/software management of a couple classroom at school, I want get my life a bit easier and part of that would consist in a Server with domain, allowing central authentication management, remote install, DHCP etc.

For historical reasons, we have 3 classrooms at different stages (not sure about the correct english word here, hope you still understand).
My idea is to put the server in the classroom which is in the middle (if I look in the vertical POV) and use a wire down and a wire up to the other classroom.

The thing is: is a single 100Mbit link OK for this? Do I need more?

There is no Internet so no bandwidth usage from that.

100Mbit/s is probably more than adequate. The only thing of the ones you mentioned that require bandwidth is serving files for remote installation.
Note that if you use roaming profiles, your logon might use a bit of bandwidth too, but all in all you should be just fine....

Regards

Grisen

Thank you Grisen.

I won't install multiple machines at once, and this is only a way to reinstall OS & apps easily when needed, so one machine by one if a problem arises.

Also, I do not intend to use roaming profiles although I may locate the My Documents folder on the server, I dunno yet ('cos I won't use a profile per student but by class and so it could allow easy cheating ...).

May be a simple Wireless network, with cheap USB Wifi can do the deal?
There are cheap repeaters for Wifi.
hide your SSID, and manage the autorized MAc address and you ll be safe. (WPA2 ?)
high gain antennas can go through building floors.

who?

100 mbit is not enough to do remote install on more than 1 machine at a time unless you have a lot of time. 1000 mbit would give you 6-7x the bandwidth.