Sounds like fun!
think you could save some weight without giving up comfort or safety.
Indeed, bring the tarp OR the space blanket. If you think it will be dry for sure, take the spaceblanket and use it as a tarp if you were wrong. If there is even a small chance of rain, bring the tarp. A 15F down bag will be useless when wet and super heavy too.
Shirts: you list:
Long sleeve button up
merino wool top
Take just the button shirt.
If that's not warm enough, wear the button and carry the merino for nights. Or better yet, if you have (or can buy cheaply, EG Stoic Hadron, MEC Lightdegree ) a down shirt, take that for evenings/camp instead at a similar weight and much more warmth. With a heavier down jkt you might be able to take the lighter sleeping bag.
On the other hand, do you have any shell? What are the conditions? Temp? Wind? Precip?
If you are bringing long underwear for nights, sleep in those and rinse out your synthetic undies in the evening, they will be dry(enough) by morning. Also, 5oz is EXTREMELY heavy for underpants, and you have 2 pairs, for a total of 10 oz.
I just weighed my 'Sonoma' synthetic boxers from JC Penney and they were 2.6oz for a size L. So, taking only one of those would save you ~7oz. I am sure there are lighter ones out there too.
Buff and balaclava serve similar purpose. Pick one. (Your sleeping bag has a hood right?
Bring 2 pairs of socks. If they are merino wool you can easily hike 2 days in one pair. Or, bring one ultralight pair to hike in, rinse at night and sleep in a warm merino pair.
Fire items are very heavy. You list 5oz. A Bic mini is 0.4 oz, my UST firesteel mini is 0.9 oz, so about 1.5 oz total would give you plenty of firestarting capability.
I just weighed my packtowel: 1.2 oz. You don't need a full size towel, that's the idea of packtowel, you can use a small piece, wring it out and reuse it.