Hi Robin,
First of all, congratulations on your surgery date! I'm kind of surprised Dr. Leis doesn't have specific instructions for this. The surgeons I consulted all had fairly strong opinions about it and spelled out what they wanted.
Here is what Marci says on her website:
http://marcibowers.com/grs/prepare.html There is a link there with a rough diagram of what the operator will need to clear. Please note, do not clear the entire scrotal sac! You will want some of the hair on the outer areas to cover up scars. (you really should pin Leis down on exactly what he wants)
To answer your other question, yes, it hurts like hell... if you don't use numbing cream. Either get an EMLA prescription from your doc, or else ask your electrologist if they have lidocaine for sale. I really didn't have a problem with the pain when I used EMLA, it was naptime. I would consult your electrologist about how to apply it. No special panties needed, just your garden variety plastic wrap.
5-6 months is a pretty short time to permanently clear that area (see Marci's discussion about hair cycles). I'm not sure anyone would guarantee you hair-free for that short of time. But with the right person, I think you could a lot of it. With your skin pigmentation, I'm not sure laser would be a good option.
Good luck, you can do it!!
mamba