Check out this post https://backpackinglight.com/forums/topic/seam-sealing-a-backpack/ before you decide that you want to actually give it a try.
If you want to seal the seams check out https://www.trailspace.com/gear/seam-sealers/ or https://ripstopbytheroll.com/pages/search-results-page?q=ultra
Can’t remember what fabric the Kakwa uses so make sure you double check that whatever you use is compatible.
I use a trash compactor bag to keep dry items in. It’s simpler.
Try using smart water bottles or similar instead of Nalgene as they should fit better and weigh less.
Either way have fun out there.
Enjoy having a lighter pack or get a https://www.rei.com/product/148036/rei-co-op-flexlite-air-chair or https://www.rei.com/product/158004/helinox-chair-zero. They are essentially the same but sit slightly different so if you have the option it’s worth trying them out in store.