Hey thats looking very nice.
Who makes the frame again, can't see it ? lol.
I know what you mean about seatposts as I am 85kg give or take a fews days after the curry house or not so never know if a lovely scandium thing is going to be safe so also plumped for a 220g one. Interesting the Thomson is the same weight as my carbon Syncros almost to the gram.
Putting a carbon rigid fork on is a very simple way to cut a huge amount of weight off but is the easy way out and would stop you obsessing over how to save another 50g here or there which is all the fun of these WW projects. Also the descents would be rather more testing, my Airborne SS with carbon rigids was around 19lbs but bounced off every pebble !
What tyres have you got on there ? Tubeless ?