I had rectal cancer and went through a similar protocol that your husband will be going through. I am single and didn't really have a caregiver except some great friends that would do a couple of things for me. I worked the entire time I went through treatment except when getting out of the hospital from surgery. Yes, the chemo can be intense but mostly, your husband will probably just want to rest and sleep. There isn't much you can do there to help!
I had radiation/chemo for six weeks prior to my surgery. Besides being tired and some GI effects, I was pretty OK and recovered quickly once the chemo and radiation stopped. I had an ileostomy in December and was in the hospital about 6 days. I learned everything I needed to to take care of myself while in the hospital. Sure, I was sore for a couple of days but also recovered quickly from the surgery. I then had FOLFOX for 8 rounds. I would go to chemo once everyone other week for about 4 hours. The day of chemo I would come home completely exhausted and sleep for a while but I was back to work the very next day.
I think you can handle grad school and be a caregiver as well. The things I needed most were rest, and someone to food shop for me. The rest I was able to handle on my own.
I wish you and your husband the best.