You may want headset wrenches, but for many older bikes just a large adjustable wrench may work well enough. Also important for working on older bikes specifically are small box-end wrenches in 5/16", 6mm, 8mm, etc for small cable anchor bolts. It can be difficult to get these properly tight without stripping with just and adjustable wrench.

Many older bikes also have different style bottom bracket tools, but for many non drive side cups a track type lockring spanner will work in combination with a pin spanner. The fixed cup usually needs the correct wrench, can't remember the name.

As for supplies, make sure to have brake and shift cables, housings, and brake pads. Replacing those parts on an old bike is often the most worthwhile thing you can do.

Fixing up used bikes from CL and selling them can be fun, but its very difficult to make money doing it.