Your buddy is probably the best guide on this! When it was being built, the pre-treatment for premium wood like this is pretty mimimal but the preparation is going to be exacting.
In your case, you strip all the hardware, strip the existing finish, sand the body to remove all the damage. No oil would be used unless you want to end up with a bare oil finish instead of the regular gloss varnish. Your buddy can make a call as to whether a colored filler is desirable on the grain, but I don't think this was done on your original koa. The grain pattern of the mahogany back of a Les Paul is often enhanced using a darker grain filler before the varnish. The entire face of the fingerboard will need to be fully masked.
After everything is immaculately prepped, it's just a lot of spray coats of polyester or polyurethane varnish and a lot of time. The only tricky part of a guitar refinish is that they will be spraying all sides of the instrument. There are a lot of curves and tricky areas (particularly around the neck joint on a through-body instrument). This is a lot of work both for spraying and sanding afterwards, but shouldn't pose any big deal to a refinishing pro.
Good luck!
David Fung