|Whew! You don't ask for much.......LOL|
Ok. Let's start at the begining. If you have a router, or router's, in your environment then you likely won't need layer 3 switches. As long as the switches you're using are managed and VLAN capable that's about all you need.
I would recommend, if at all possible, to have a structure as follows:
Subnet = xxx.xxx.1.xxx = VLAN 1
Subnet = xxx.xxx.2.xxx = VLAN 2
Keeping the tags the same as the subnet as you can see will make life easier.
Your management VLAN will encompass all network appliances. Which is to say, switches, routers etc. You want this separated from the rest of your environment and you most definately don't want regular users on the management VLAN as it's sole purpose is to allow you to manage your equipment. It's very handy to be able to remotely manage switches and such. It saves a lot of running around.
Then you have to decide on how you're going to separate things. Do all 30 rooms need to be on their own subnet? Personally, I don't think so and I feel this would cause a lot of extra headaches. Typically separation is more along the lines of:
VLAN 1 = management VLAN
VLAN 2 = servers
VLAN 3 = printers
VLAN 4 = clients
Keeping in mind, a VLAN is a subnet.
You can also segment off more sensitive areas to reduce access. Accounting is a prime example. You might want all finance and accounting people to have their own subnet so that other members of the business have no access to their data.
With technologies like VoIP and/or video conferencing, you will want to employ QoS (quality of service) so as to ensure they get the highest priority. If you don't have a separate QoS device, you can purchase switches that do QoS. Personally, I like using both. The QoS device on the main access point for your external connection and then QoS capable switches so you have more granular control at the user level.