Water Treatment: You mentioned that you're doing an early NOBO hike leaving in March. If you stay ahead of the crowd and all their waste, you may not need water treatment if you pick good sources.
If you decide to treat, consider AquaMira or chlorine dioxide tablets. Either is much lighter weight than a filter or a Steripen and you can resupply them in a bounce box or your food resupply box if you're going the food mailing route.
You could even do a hybrid approach whereby you carry a small amount of tabs or drops and treat only if you think the water may be sketchy and otherwise don't treat.
Sleep insulation: Many cottage manufacturers can make you a 20F quilt suited to your sleep style for less than or equal to the cost in dollars of the WM bag and about 9oz. lighter. This is a good place to drop weight for the same amount of money. If money really isn't an obstacle, go crazy with it and get a quilt custom made with breathable .33 cuben fiber and eider down.
Shelter: I would ditch that tent and go for a poncho tarp. Shelter is a very personal choice just like water treatment, but there are some empirical advantages to a poncho tarp on the AT especially.
This will double as your rain gear and shelter. Keep in mind you will have the option to sleep in a hut every night. Even if you prefer to not sleep in the huts, if you just slept in them on heavy rain nights you'd do well with a poncho tarp. Tents tend to turn into dead weight or will be mailed home. Even if not used as shelter ever/often, the poncho will still be used often enough as rain gear.
As another poster mentioned already, if you really do want an enclosed shelter, go with a cuben fiber Hexamid from ZPacks.
At the very least ditch the ground clothe or go with a polycryo ground clothe.
Portage: If money really isn't an obstacle, pick up one of the new Exo backpacks. If you ditch the Kilo, go with a torso length inflatable, and switch to a quilt, volume shouldn't be a problem and the Exo offers many options for temporarily hanging stuff on the outside until you eat some of the volume after a resupply.
It wouldn't be needed if you go with the Exo, but consider using a fumigation bag as a pack liner. These have the advantage of being both lighter weight and odor proof by design versus a trash compactor bag or other pack liner/cover.
You don't have a first aid/personal kit listed. This is important and for an AT thru should include doxycycline in my opinion. If you're bit by a deer tick or you start coming down with lyme symptoms it can be important to start treatment immediately. You will need to get this prescribed to you by a physician before you head out.