Gardens aren't very efficient for Happiness. Happiness will be getting a rework next update and I think I'll move gardens to just be decorative.
Road upgrades are totally possible, but they would be incredibly tedious right now.
For fuel sources, things like bakeries could burn all sorts of fuel, not just wood. I'm not sure that tracking fuel usage for bakeries would really add anything interesting to the game. Maybe for Bronze Smelters, to help reinforce the idea of Bronze as an advanced and expensive material.