I like the idea of special buildings but I think linking those buildings to a town would be a good way of implementing this. You would need to build the rig and then assign it as one (like shipyards I think) then you need assign it to a town. This way you could generate the oil as a town resource without being in the required biome to discover it, you would also pay an initial investment cost into the building to generate it. The oil could be determined by the amount of rigs you own and how advanced the rig is? Also if you are occupied you’d get taxed on these resources or if you are in a nation

Also there would need to be more uses for oil as you said like it being fuel in movecraft (idk if it already is) and there should be more uses in general also the amount of energy you from the combustion engine and the required energy to turn the oil into fuel would need to be increased to cope with the inflation of oil on the server

Engines for movecraft would need to be a block that could get retexured that is a a container and that isn’t used / rarely used in nations to work well as a new blocks for the plugin

Different blocks that modify the stats of movecraft crafts could be a way to make the engine parts you mentioned and if they require resources that use oil then it would be a good way to get the oil out of the system

Just thought of a tire blocks that uses oil to make into rubber. Maybe a rubber plant tree that could get added for a natural way to get rubber.

I think NPCs would be cool but making a good system that works autonomous or under player control would take some time and coding skills. Also idk if that will end up true but npcs might be a strain on the server because they would need to be loaded around players and they would take up data (processing power and storage )

If oilrigs and other mutliblock structures like refineries where to be tied to the towny system then making more resources like iron or coal be tied to iron mines and coal mines etc a good idea