I would suggest you save 400 DCs for the real gems of the TP. Spica and Chydis. Both are great at their roles, are staples in the TP and easy min-cost targets once you play long enough. (there is also a princess if you lack a duelist)
The rotation comes every 25~ days.
(I am farming DCs for the princess, saki and AW faries myself..so much to farm so little time)
For AW orbs, i have 2 AW-ed units now and i still have problems 3 starring some AW orb dailies.
I first got orbs after CCing 6-7 units. Basically when you get your core team.
https://www.youtube.com/watch?v=XDMAdtLnKQM
Here is an example of the easier orb maps
Sidenote: hope you are rich, because you need to save gold for AW. 200k for gold, 250k for plat, 300k for blacks