Hi buddy!
Well, you already had some pretty good info but I,ll put my thoughts here as well... I'll break out the upgraded in 1) Expensive one and 2) not that expensive one and prioritize them in each category
1) Expensive upgrade
a) 160mm fork: You can find RS Lyrik Solo Air fairly cheap on some websites
b) Wheels: On that same website, Hope Pro II Hubs are cheap an because you want to keep it on the light side, pairing it with NoTubes Arch or Mavic 819 (UST) - 717 could be a good match.
2) Not too expensive upgrade:
a) STEM!!!!

b) Tires: Because you like light stuff you could have a look at the Schwalbe Nobby Nic 26 x 2.25 Evolution Line that are weighting at 540grams each.
That being said, keep in mind that you will have a blast on you new rig with or without the upgrades... Forget about people that tell you that "you really should do this and this..."! Just enjoy your ride with time you'll get your dream bike!
Enjoy your new bike!