Okay let me explain you something
Wifi is half duplex
Also just one client can speak to the AP at once...
Everytime a broadcast happen none of the clients can transmit! which is your problem...
Now are you sharing those wireless networks with Wired networks... let say
Student network you got wired and wireless users in there? because if you have it like it its recommened to have just wireless network in a vlan... and do not mix them....
As for the size of the network well
it is recommended a /24
You could build a vlan pool with named vlan for example
Student
with 10 vlans of /24 all pointing to a named vlan with the name students....
You should not go up of 10 vlans.
There is something that the HD reference guide says
Keep each VLAN subnet within a VLANpool to a 24-bit subnet mask.
Do not have more than 10 VLANs within a pool so that broadcast or multicast traffic does not consume too much air time access
Now my question to you is:
How Many users are on Wifi SSID? are they 3000 equipments?
How many users are on the student network? are they 3000 equipments?
Answer me those questions to help you more...
Also i copy you something really useful for you
Read that also it will help you :)