The radiation starts out not too bad, and gets progressively worse. How much worse varies by patient. Some sail through it. Some of us feel like we're gonna die. Most fall somewhere in the middle. There's a weird plateau effect where you think it's okay, and then boom! Your taste and stuff drop dramatically. You'd think it would taper down, but mostly it doesn't, it just drops one day. Maybe not for everyone, but it's better to know it might happen and enjoy all your favorites as long as you can.
Whether it hurts or not, your body is fighting and healing, and that is INCREDIBLY draining. Fatigue will kick in at some point for most folks, and that's something he'll want to factor in. It'd be great if he could work the whole time, but it's smart for him to go ahead and schedule back up for those last few weeks, and for possibly a couple months after, just in case. (Better to have a plan you don't need, than to scramble at the last minute while you feel like crap, you know?) Radiation continues to work long after the actual final treatment, which is something most of us forget to factor in when we're planning out our time.
Calories, calories, calories. If you haven't yet seen one of Christine's posts about nutrition during surgery and radiation, hopefully she'll pop in and give you the details. As much as possible, follow her advice. I was one who struggled with nutrition (even with the feeding tube) and it really does slow down healing.
This is probably one of the only times in his life that doctors will tell him to snack and nap as a real bona fide prescription ... tell him it's okay to enjoy that. He's gonna need it. And if not, do it anyway because he deserves it.

And if he does experience undue pain, it's okay to ask the doctors for something to help. They actually will try. I waited longer than I should have (I didn't know there were more options for pain management than what I already had). It never hurts to ask.
We'll be rooting for you both!