Installing a fork of Linus of completely unnecessary. There are many things you can do on you Mac to secure it if you think your school is monitoring it(even though it’s highly unlikely)
Disable all forms of remote control/monitoring
The first thing you’ll want to do is disable all ways the school could monitor your computer. These include VNC and SSH.
To disable VNC and SHH go to System Preferences -> Sharing, then uncheck remote management, Screen Sharing(VNC), and remote login(SSH).
This will prevent the school from controlling/monitoring your computer IF they manage to acquire you username and password.
Use a VPN to encrypt internet traffic
If one of your concerns is that the school is monitoring your internet traffic, you can use a VPN to encrypt you internet traffic until it is outside of the school network. You can do this using a service called a VPN(Virtual Private Network). With a VPN, your computer will encrypt all internet traffic when sending it, and it will only be decrypted once the VPN server which is outside of the school network receives you computers internet traffic. This will prevent the school from viewing your internet traffic(both inbound and outbound traffic).
The first way to get a VPN could bring paying a monthly subscription for one. You can usually find one for fairly inexpensive online, I would suggest checking reviews on a service before using it though.
The second way would be to host your own VPN server at your house. All you’ll need is a old Mac, internet and $20. I found this link from Life Hacker explaining how to make the server and how sign up for a DDNS service so you can connect to the server. It also includes everything you need about port forwarding on your router.
Note: A VPN will only protect WAN traffic, it will not protect any LAN traffic. Using a VPN will also cause errors when your computer tries to communicate on the LAN network.
Install a anti malware program
One of your concerns was the school installing spyware on your computer and using it to monitor your computer. One of the best ways to prevent this would be installing a anti malware program on your computer and running a full computer scan. This will check your computer for malware, and after it’s done scanning it will monitor it for malware. I recommend using one called AVG. I personally use the free version which works fine on my personal laptop. I will add that it is very unlikely that the school installed malware on your computer as that can be very complicated to do.
All this advice and different methods are only if your the owner of the computer and it’s not a laptop given to you by the school for the year. If it’s a school computer it most-likely has settings in place to prevent from disabling settings and adding a VPN. They will also most-likely have settings installed so they can control and view the computer.
Hope this helps you with securing your laptop