This is really important. If it's an old shop that still has old style wired fuses, get in a sparky to update it with circuit breakers and check out the wiring. You're going to be adding stuff to the load so you don't want problems here. Most modern leases insist on an electrical inspection any way. The cheapest form of lighting has got to be florescent tubes, but they don't really do a lot for lighting up your display. You also have to remember to renew the tubes every few years as they do tend to weaken. There's an enormous range of light fittings available so it's worth shopping around and taking some advice to get the right fittings for your shop. When i photographed my shop from the other side of the road, it looked as though all the lights where turned off. When i do a coffin spray in the shop it looks nice and full, but as soon as i take it out into the daylight, i can see all the gaps. So maybe have some extra spotlights that you can turn on when you are doing things.