cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
Are you looking to specialise in network security, or stick with core network/infrastructure deployment? I'd suggest looking into some firewall solutions (Smoothwall, pfSense, Cisco ASA/PIX), maybe an IDS/IPS solution such as Snort; you could get some Cisco routers, switches, and ASA firewalls from eBay if your teacher isn't too concerned with where the equipment comes from.
As for hosts, virtualisation may be the way to go if you have a small number of people in the labs; a native VMM like VMware ESXi or Oracle VM server would allow you to create and teardown VMs as needed. ESXi in particular runs quite well on the HP microservers; you install ESXi itself onto a USB memory stick, then use the HDDs to store the VMs.
As for (ethical) hacking, BackTrack is a good way to go (man in the middle/browser attacks, smurf attacks, ping of death, ping pong attack, teardrop attack, land attack, port scanning, network mapping, OS fingerprinting, (D)DoS to name a few). If you're looking to do wireless cracking, you will need a wireless adapter that supports rfmon mode.
I take it you want to go for an enterprise equivalent network, so I can't say I would recommend going for a Linksys wrt1900ac it seems too consumer to be any use to you. I don't think I would see it being used in an enterprise environment, instead pick up a cheap Cisco router and some wireless access points. I don't really see what you will gain from having AC APs in a test environment its just overkill in my opinion.
Something you might look into is a virtualization server, that has allowed me to "play" with a lot of different things I wouldn't have been able to play with otherwise. I run Proxmox VE on mine, but even something as simple as PHPvirtualbox would probably work, sadly I think I'm going have to jump ship because Proxmox is becoming less and less free...darn XD