What bullets are you going with? Also, what scope did you get? Reason I ask is I know most of the scoped CVA packages come with a 3-9X scope, which I find too much for around here. I bought one with open sights, figuring if I want to add a scope in the future I'll put a 1-4X24 on. A close up shot on a deer at the lowest magnification with a 3-9 might just show up as one big blob.
As for sighting in, have him shoot groups at 25, 50 and 100 yards if possible so he can see his POA/POI at different distances. In the offseason you'll have more time to tweak it where he get can his sights set in so he may just have to aim at one spot from 0 - 100 yards and have a hit on vitals regardless, just so he doesn't have to be thinking of where to aim at different distances. My routine to sight in was to blast off a primer on an empty barrel to clear any residue from cleaning, etc, load, place in a new primer, shoot, remove the breech plug (CVAs generally have the Quick Release plugs with makes it easy), spit swab, dry swab, replace the breech plug, blast off a primer, load, new primer, shoot etc. I opted to swab between shots just for consistency when sighting in, but as
@Mark from MA stated, as long as you swab every few shots you should be ok, particularly with the cleaner black powder substitutes. When loading with the ramrod, make note of the position of the rod when it's loaded, and make sure it's at that point each time so that you know everything is fully seated, and that you didn't double charge. Once people have the bullet/powder combination they like, they'll put a witness mark on the ramrod. Loading a ML is pretty much loading ammo; you really need to have a set routine and pay attention. Take time between shots so that you can let the barrel cool down if needed, make target adjustments, clean up a little etc, then when you're ready to go load and shoot. And remember, the primer goes in after you have loaded the ML and are ready to shoot, not before. I don't say this to insinuate you don't know firearms safety, but it's almost natural to put in a new primer when you're removing the old one, especially with a break open inline.
As for your the new hunter, you know him better than anyone else in regard to the amount of time they'll be able to sit before boredom sets in. When I go out it's generally in with a headlamp on and then out with a headlamp on. My 17 and 19 year-old sons would not want to spend that much time out in the woods. Hell, I couldn't sit that long at their age. Now that I'm older, I use it as an opportunity to enjoy the peace and quiet of the woods. Check in with him every once in a while, and once he says he's had enough, or even if you think he has had enough but might not want to say something, pack it up. Even if as a hunter you know primetime movement could be another hour away, if he wants to go, go, just so he doesn't get turned off by the whole thing. Maybe even prep him a little as to what to expect, or not expect, just so he doesn't think the deer are zipping around everywhere out there.
I know a lot of this has nothing to do with ML, but figured I'd throw it out there. You probably know most of it anyway. I think it's great that he wants to head out there with you. I really hope he gets something, or at least sees a whitetail out there. Good luck.