1. That really sucks and I'm sorry you lost that school.
2. When big mistakes like this happen, I typically overreact and begin making several different fail-safes. Overflowing a tank is probably the first big mistake a person makes. Getting a float valve and shut off for your water hose would be a good idea.
3. RESCUE! RESCUE! RESCUE! If you are anywhere near civilization, you can get fish who have outgrown their homes for next to nothing, including Niger catfish, RTC, and Pacu. Take your time and let the fish who need a home like the massive and awesome tank you have find you.