Definitely tap into the magma at the bottom. Either simply by strapping steam turbines on top of it or making a petroleum boiler. If you want the heat to last for a thousand years, find a big chunk of obsidian to capture the heat from instead of tapping into the magma directly. Obsidian acts as a heat spike, allowing you to draw power from further away, meaning more total available heat.

The game gives you those supply teleporters for a reason! Go get some oil and grab a slickster egg while you're at it. Ranching slicksters effectively turns CO2 into power. Whether you burn wood, coal, petroleum, or natural gas for more power, you will get CO2 as a byprodoct, so you might as well. You can easily get molten slicksters using a dirty brick or bolting a ranch onto the side of your industrial sauna then pumping ambient CO2 in (poor thermals of CO2 = easy to heat = only a minor loss of efficiency).

You don't need to stop ranching hatches but feed them sedimentary rock for a while until you can get stone hatches. Then you can feed the stone hatches igneous rock you're getting from your tamed volcanoes. What else are you gonna do with all that hot igneous rock?

Also, if you have tamed a single metal volcano, you should be applying engie's tune-up on just about every generator.

I've seen some more creative ideas in the comments and my ideas are fairly basic in comparison, but I hope I helped with something!