Daox,
Since you're retrofitting and want/need a good "bang for buck" ratio I'd suggest:
1. Run conduit and rewire for everything you can imagine wanting or needing.
2. Insulate the foundation perimeter to reduce the garage slab heat loss. I know how cold garage floors can be in the winter and limiting the heat sink effect should help. A large carpet remnant can also really help with increasing comfort in the garage.
3. Run 2x2 stringers horizontally across the 2x4's (
http://www.builditsolar.com/Projects...MooneyWall.htm) install insulation mesh, blow in (borate-only) cellulose insulation, install drywall.
That should make your garage MUCH warmer and more comfortable in the winter for a reasonable cost.
FWIW,
Tim