Fiber network , what protocol to use ,after Dark fiber from ISP (or any fiber)

Hi Everyone:

Im doing a project for my university and im stuck on this. I talk on the project about how fiber works and blah blah, now comes the network part (which i dont know too much) and i need to decide how to create my own network after i get my fiber connection.

Lets say i want to haul fiber to a town with 100 people. it will be GPON , im still stuck on what L2 and L3 equipment i need(its in progress) but now i want to focus on what protocol do i use.

BGP? OSPF? IEGRP? , do i use MPLS? do i need to think in the future in case i need to haul to another town with more customers?, does the ISP needs something from me to connect to their network? peering?

I know fiber its expensive(digging and all that) but its been a fun project so far.

Thanks and regards too all the amazing network people on this sub!