#1
1st Question - - - Is it absolutely necessary to sand down to the wood to give a guitar a brand new paint job, or can I just sand off the old paint down to the primer?

2nd Question - - - How the hell do you sand down in the pick-up cavities and where the wires go?

Thank you for putting up with my noobish questions over the passed week, im sure there are more to come.
#2
you only have to sand off the clear finish. just make sure before you start painting, the surface is really smooth. as for the pickup cavities, you don't need to sand themunless your gonna see them when it's all finished. in which case, i don't know..