+1 on the Mountain Hardware Power Stretch Gloves. On REIs website they seem to get mixed reviews but I love mine. Very comfortable, warm, and no awkward seam placement. I wouldnt say they are winter stand-alone gloves but for JMT temps they are perfect. I didnt take gloves on the JMT and was fine with using the handwarmer pockets on the down jacket, though I wasnt using trekking poles either.
I did the JMT with a generic beanie and loved it as well. I liked pulling it down over my eyes to shield morning light and for extra warmth. It seemed like it got bright at 5AM for some reason. Helped with getting an early start though.
A friend I walked the trail with LOVED her OR Sun Runner hat. I am planning on doing the JMT again this summer and I am definitely taking a hat with similar sun protection. When I got back, not only did I smell like a bum, I was also tanned like one, even after much 30 SPF sun screen application.
You should be fine with one pair of chonies.
I didnt take a separate shirt to sleep in as a personal preference. I was dirty and I stank, no two way about it. I was fine with washing my bag after the trip- something you should consider either way. Depending on your bag the montbell down jacket should be enough if you get cold at night.
The longjohns are a must however. You dont want to wear rough convertible pants to bed, its just not comfy. Still, I slept with the shorts section of my convertible pants in the foot of my sleeping bag becasuse they would be ice cold in the morning and I just didnt like that.
Sorry if this was wordy, hope some of that helps. Cheers!