I don't think there is any one right way to bring gear - but here are some thoughts. I hiked the trail a couple of years ago and would do things differently this time around.
I'd wear a hat with a wide rim in the desert and possibly a cord for under your chin for it does get windy. I think anything that provides shade and relatively good coverage would work.
Balaclava: I honestly found it nice to have in the north, starting around mid-Oregon. But this is really a function of many things: your speed, off days and the such - the later in the year you push it, the colder it gets with a great possibility of wet and cold weather. I used a thin fleece one, worked well ehough. It was very lightweight. Was it a necessity? No, but it was nice when it snowed.
Sun gloves - This is a preference thing...I put on a ton of sunscreen and went that route and was okay. Some people swear by sun gloves, for me, I swear by heavy duty sunscreen. I still developed an incredibly dark tan over time (and I am a pasty white guy).
Long pants - i used convertable, but honestly, get whatever is light if you go the long pants route. I hiked in shorts sparingly - in the desert the pants helped with all the thorny things and minor scrapes. By the time I got north, I was just used to wearing long pants.
Gaiters - Again, a preference thing. They do help keep dirt out of your shoes. A lot of people loved them. I didn't use them, but I'd try it out next time. I opted for breathable shoes that ended up allowing a lot of fine dirt/sand to pass through, so I don't know if the gaiters would have helped me much.
Mitts/gloves - I personally like gloves because my hands get cold. It was nice in camp. I don't think you need anything super duty, but by the time I got to Washington, between cold rain and snow, I carried multiple pairs (I know, it make me a heretic on this site) so I could swap out the wet ones for dry ones.
Groundcloth - I slept directly on ground plenty of times. But there were thorns in SoCal which can play havoc on the your inflatable thermarest. In the north it can just be wet. Those polycro groundsheets weigh very little. http://sectionhiker.com/gossamer-gear-polycro-ground-cloth/
If you haven't used a polycro groundsheet, they are at first very clingy, but after a couple of uses that goes away and they become a snap to fold. I always put a small piece of tape on the "UP" side so I can keep the same side to the ground.