The WB Wooki has an integral underquilt protector. Is the concern wind penetration or rain splash? If cold is a real concern, I would consider stacking your underquilt with a ¾ length 20° F underquilt. I use a JRB Greylock 3 with my SLD Trailwinder 40°. It can also be stacked with my 20° top quilt.

I find the WB Eldorado mosquito net adequate for wind protection. I suspect a top cover would be too claustrophobic for me. A WB XLC or Eldorado top cover is $55~$95, why not try it?

I have not hiked the AT but suspect the 20° UQ and TQ are adequate. A puffy jacket should add additional comfort. I use a fleece stocking cap and puffy booties for additional warmth. Some like the JRB Down Sleeves.

I like the idea of a 1/8” foam pad as a lightweight multi-function accessory.

I think your tarp should work fine. You could add a 2QZQ GRIZZ BEAK from Dutchware. These would be a simple DIY project.

I would take a couple of weekend shakedown trips to test your real gear needs.