I thru-hiked the AT in 2011 so I thought I could add a few thoughts. Your list looks great and I’m sure if you didn’t change a thing you’d be happy and safe. A lot of the comments so far are spot on in my opinion.
Rain covers are pretty useless and not many people kept using them after the first couple of months. Pack liners keep stuff dryer and you don't have to quickly pull off your pack and throw on a pack cover when it rains. I saw so many people with pack covers hanging off their bag and they had no idea until someone behind them pointed it out.
I would think that the ULA pack would be fine for the whole trip. You won't need to carry huge amounts of water or food so your packweight will be relatively low even if you add more gear. I hiked with a base weight of 13lbs with a frameless pack and it was perfectly comfortable.
I started my hike on April 4th so it may have been warmer but the clothes you list would have been adequate. Just a down layer would worry me too. I had a synthetic top and a synthetic vest and I really liked that combo. I never needed to hike in anything warmer than the vest. I would consider long johns because they are a guaranteed dry layer to change into when you get to camp. I would also consider a rain skirt instead of pants. I haven’t tried mine yet but everyone who had them swore by them. Whatever you carry for clothes, make sure you have something to change into for laundry days. I.e., keep the windpants if you go with a rain skirt. I would rather carry a windshirt over a long sleeve shirt. Weighs less and provides better warmth.
I agree with the air matt comments. I started with a ridgerest and switched to a thermarest prolite as soon as I could. Sleeping on a hard shelter floor sucks with a ridgerest. I would scrap the silk liner in favor of a bivy sack if you go without any mosquito netting. The bugs were bad at times and you can use a bivy in the shelters as well. Even in my ray-way net tent with flap closure I got some nasty bugs, including rolling over a millipede in the night and having a beetle crawl up my pant legs while I slept.
I would hesitate to use the trailstar. My ray-way tarp was too big in a few situations and the trailstar is even bigger, I believe. It wasn’t a big deal if I was stealth camping but it was an issue in camps. They often had designated sites for tents and they were not big enough for my tarp without creative pitching. I also felt like I was taking up more than my fair share of room in a few tight situations.
I would ditch the titanium cup and get a folding coghlan’s one. I know it’s small but it’s light and I barely ever used a mug (very few people took the time to make a hot drink) and when I did, it was for booze or an instant coffee which is only 200ml anyway if you use the little sticks of instant. It takes up very little room, it’s super cheap and (this is the real reason) it’s flexible, which allows you to collect water from difficult sources. You can press it up against a rock with only a trickle of water or dip into puddles that are only half an inch deep. I found I could get water from sources that other people couldn’t. 4 oz is pretty small for a fuel bottle. The fuel resupply places are spaced apart sometimes. I carried an 8 oz I believe. It was just an old water bottle. Lasted the whole trip. No bear bag rope?
Sea to Summit lightweight dry bags aren’t waterproof. I still used one for my small ditty bag but don’t rely on them to keep important things dry.
Lots of people did it, but the trouble with using an iPhone for your camera is that you’re killing your cell phone battery every time you take pictures. Guys would call their girlfriends sometimes and kill their battery then couldn’t take pictures.
I agree with ditching compass. The trail is really well marked and winds so much the using it to determine which way to go can be foolish anyway.
Finally, out of every piece of gear I misjudged and everything I wish I had done differently, the one biggest item I wished I’d taken was an eBook. I got one that July and I loved it! It was pure joy to have limitless reading materials every night. It saves your sanity when you are stuck in a tent in the rain for half a day and it gives you something to look forward to every night, especially if it’s been a really rough day.
The most helpful thing I found when I was preparing for my trip was talking to an alumnus on the phone. You can get so much more info, ask questions and get answers to questions you didn’t think to ask. If you’d like to chat, PM me and I’ll give you my phone number.