Blank canvas, steel sided 40x60 pole barn. Thoughts on insulating, electrical, heating???

While is may be more up front. With the right spray foam you could heat the entire building with a candle (slight exaggeration).

You could use drywall if you put backer boards where you know you need support.

If it is humid in your area use moisture proof drywall, and paint with proper primer and paint.

Electrical. You could install conduit at floor level and at 8 feet up all around the walls. Put junction boxes every 4 feet or so. Use oversized conduit to allow for changes down the road.

Heating / cooling, put in whatever is the most efficient. Propane / electric etc.