I've just crafted my GF (with no UVs sadly), and that leaves me with 3 gears to be upgraded.
Which of these three should I craft next? I don't have any recipes for any of them, so I have to buy them first, but polaris will take some time to find.
Keep in mind I only have enough CE to craft one more 5* gear.
Other options (if necessary):
Shadow Alchemer line
Glacius/Shockburst line
Haze/Static Bomb line
BTB line
The other options I do not have the 4* version to, so I may not be immediately able to craft them, but I think I can squeeze some CE out just for one of the lines above. The main three I have just enough CE/cr for.
We can't answer this question without knowing what your other main weapons are. Are you saying that you have these high-star weapons, and no others?
* Gran Faust
* 4-star Umbra Driver
* 4-star Glacius
* 4-star Voltedge
* 4-star Voltaic Tempest
* 4-star Barbarous Thorn Blade
* 4-star Polaris
If so, then you'd be nuts to upgrade Umbra next...you want to diversify your damage types. That means piercing or elemental. Do you like to play with swords, guns, bombs, or a mix? Which mix? We know almost nothing about you.
While we wait for some information, I'll go out on a limb and say (A) Barbarous Thorn Blade (piercing swords are very powerful) and (B) either Voltedge (it's better than Glacius), Polaris (an elemental sidearm gun is a useful thing to have), or Voltaic Tempest (it's a great crowd-control bomb).
And although you're using up all of your CE, keep in mind that you can always get more CE with crowns. You just have to save up a bit.