How should I propose and set up IT support for our small school?

I teach at a small private middle school in a developing West African country, and over the past two years I have gradually become the person responsible for most of the school's technology. I originally studied software engineering before becoming a teacher, and although I am still learning networking and systems administration, I have been building a small homelab and improving my skills with documentation, tutorials, and experimentation.

Our school now has a computer lab with 10 desktop PCs, but the lab currently has no proper network equipment and only unreliable Wi-Fi. I have been maintaining the computers, teaching basic technology classes, and making manual weekly backups. None of this was included in my teaching contract. The school has also purchased a small 3D printer, and I requested a 24-port switch and related equipment so the lab can have a proper local network. Those items are still being shipped.

I want to approach the CFO with a proposal for a separate, paid school IT or sysadmin role alongside my teaching contract. Taking on this work would reduce the time I currently spend tutoring after school, so I need to negotiate fairly despite the school's limited budget. I would appreciate advice on what responsibilities should be included in the proposal, how to structure compensation, and whether the school website should be part of the ongoing role or treated as a separate project with a one-time fee.

I also need guidance on the practical setup. Should the lab remain on Windows, or should I consider Linux? Would Active Directory or individual student accounts be worthwhile for only 10 computers, or would a simpler setup be better? The school has no server, so could I repurpose a desktop or laptop for backups and other services? Since power outages are common, I am considering a UPS, surge protection, and possibly refurbished hardware with redundant storage. Beyond the lab, should my proposed duties include managing staff computers, backups, archiving, networking, and basic security? I want to keep the design affordable and maintainable rather than creating a system that is too complicated for one person to support.