If you add chips on teh edges of your model or use pencil to represent metal should/do you drybrush over that? Or db teh add graphite edgeing? Pt 2 when using camo do you drybrush one colour for teh whole model or use lighter shades of teh camo colour?

Paint chipping or bare metal should be done last. If you drybrush after, you'll cover up the effect of the bare metal. And when drybrushing, I usually use a lightened version of the base color. I do try to keep the effect from coming out too strong on the camo colors. This method also helps to tie the colors together and tone town harsh differences between colors. If I have a paint scheme with large areas of color, I might drybrush with a lightened versin of each camo color. On the real thing, the camo colors would be worn off and faded first to reveal the base color underneath.

Dry brushings goal is to highlight detail so it should go last. And 'over chips' is up to you as far as how you want it to appear. You may want to dry brush the edge of the paint to show off the chip more. Depends on how old the chips are too. Older ones may show more wear and may be dirtier etc.
As far at Pt 2- not quite sure. For multi-color camo I usually airbrush the base light color. Mask off what I want to remain light, then go to the next darker color. Spay that, the mask both off and go to the darkest color. For modern three color, I do OD first, the brown, then black. If I want a hard edge I mask with masking tape. Soft edge, I use an elevated mask. This is where cut card stock to mask off an area or shape, then I hold the mask above the kit about 5mm and spary directly down at 90 degrees. The 5mm allows some overspray to blurr the edge between the two colors.
I don't drybrush my camo schemes. If others do, chime in, let us know how you do it.