Definitely insulate it if you go steel or the metal will sweat inside when there’s a big temperature difference between inside and outside. You can save a lot of money if you do the insulation yourself, then put up plywood/OSB walls. Electric would be nice and you could consider gas or propane wall units for heat. If you’re putting a workbench in there, heat and electric would be great to have when you’re doing projects in the winter. You’ll save a lot with site prep because you already have the concrete in place. Also, LED lights are way brighter than fluorescent lights and are inexpensive.