1500-2000 devices using the guest network? That number sounds very high (not knowing what school you are / location). For example, we are a K-8 school with 700 students, about 1500 devices in our entire network, and my guest network only has 5-25 users at any given moment. We don't have guests roaming the school, and on the church side the number is small. Also, I have guest turned off on the school side during school hours.
This is a High School. We created a Guest SSID with a different VLAN just for them with limited bandwidth for their personal devices. I agree this is a very high number hence, I'm looking to put in place all the relevant advise I can find in this community.