Ken,
You want a gloss or at least semi gloss before you wash. You want a smooth surface so that the wash only really 'sticks' into the recesses, and the excess can be wiped off of the smooth areas.
Colour is up to you and the effect you want to create, Based on that colour, I would probably start with brown and see how it looked, you can always go darker if you want to, but really tough to lighten it.
For panel line or pin washes, your wash should be thin and applied to the recesses as closely as possible, then the excess wiped away. So, with the thin wash, you'd touch your brush to a corner of a panel and let the fluid run along the grooves, and repeat as required.
Wipe away once the wash is dry (it should take on a dull look to it).
This might also help a bit: migproductions.com/.../washes-and-filters
It's an art form, for sure. It's very easy to talk about how to do it, tougher to accomplish.
I hope that helps.