(To answer an almost guaranteed question, I do plan on doing FSC a lot)
I have 1600 CE. I am making my Avenger into a DA, but what should I do with the other 800?
Grand Flourish-Final Flourish
Strike Needle-Blitz Needle
or Ascended Calibur-Levi Blade
I can't decide.
From what I've heard, Blitz is one of the most popular weapons in FSC. I'd suggest upgrading that before the flourish, and not upgrading the calibur at all. The upgrade from ascended to levi is mostly cosmetic, and for someone who is at least partly a swordie, normal damage swords are not very useful anyway.
Parties, yeah. I can only afford to upgrade one of those, and that will prob be the strike-blitz.
DA is a great idea. You predicted only part of the question. Are you going to do FSC in parties, or solo? My guess is in parties.
Then you will be valuable if you have Blitz Needle (or Shivermist Buster), because many parties run their Vanaduke tactics through these two weapons.
Final Flourish is great for killing trojans, but if you're in a party then Blitz is even better; charge up while your teammate distracts, and then unload.
Leviathan Blade is respected for phases 2 and 4 of Vanaduke (the mask phases). But any sword is good enough there, and Levi is not especially useful anywhere else in FSC. I'd recommend that you just forget about Levi.