Hang three rows of flourescent lights, then paint the walls and floor High Gloss white. You can never have too much light in a shop. You'll need a good sturdy work bench that's high enough that you don't wreck your back working with parts on it. A drill press, a hydraulic press for bearings, a grinder with wire wheel, a small wire feed welder if you're flush, some gas bottles, a good rollaway tool box with everything from torx bits to metric allen wrenches, sockets and box end wrenches, a small air compressor, a deep sink if you can plumb it and a beer fridge. I also have a recliner in mine that a neighbor was going to toss but you might be cramped for space so that's optional. Some kind of radio or CD player....a dart board is fun...
For lighting, just make sure you have two flourescents, one on either side of the bike. If you only have one centered in the shop, your bike will live under it in shadow.
A Petzl LED headlamp is great to provide light right where you need it-- even if your shop is otherwise lit only by a single bulb.
As for tools, you don't need many for working on dirt bikes. I fit all my tools in a small rally box so it's easy to bring to the races. A small T-handle set of 8mm, 10mm, and 12mm. An allen head set. Your bike's stock toolkit. A small flathead and small philips head screwdriver. A dead-blow hammer (and/or wooden mallet) and small pieces of wood or dowels for knocking out bearings and cylinder heads.
For pricey items: A good torque wrench, that will register small torque values. A good impact driver would be nice to have, but I don't have one and still get by.
I occasionally use other tools, such as random sockets or wrenches. You probably already have a set of sockets and open-ended wrenches anyway.
Two long tire irons. An accurate 0-30psi low-pressure gauge. Baby Powder. An air compressor.
How about a sink or parts washer, something to wash air filters in?
If your budget is really tight, get your fluorescent fixtures from a building wrecker/recycler. Stick with the 48" like the man says, cheap, last forever, available everywhere. If you buy weirdo non standard lights and fixtures you will have problems when it comes time to replace. (DAMHIK)