Looks good so far. Some thoughts:

• Stratus Dancer could easily be replaced with another counterspell. It's a bit slower than you'd like and has to be played at sorcery speed.
• Reflector Mage is an awesome card... I'm just not sure it goes in U/W Spirits. He has to be cast during your turn, and the time he comes down is the same time you want to be holding mana up for other things. Use Unsubstantiate instead.
• Essence Flux is just... cute. It can very easily be a dead card, so I think two is the maximum you'd want to run. Zero is fine. I'd replace some of them with Anticipate.

Thanks for the feedback ComradeJim270!

Stratus Dancer is a test to see how it plays out. It flies, is a 2/1 and if needed can be morphed to counter something at 2CMC. It's not a great card per se, but it might have a role to play. I may very well end up taking it out before gameday. I'll confirm that tonight at FNM.

Reflector Mage is there because sometimes you just need to bounce something and not see it for a while. It's also a great sac for Elder Deep-Fiend. The things I like beyond that over Unsubstantiate is that it leaves a 2/3 body and the bounced creature can't simply be replayed. Of course Unsub has it's own advantages too. That's why I like to have access to both. I'm testing with 2 now to see how it works out. It's possible that I may end up moving 2 Unsubs from the side to the main and replace them. I'm not sure about that yet.

Essence Flux is just an amazing card. It's not just cute imo. Targeted removal is very popular in the meta. Dromoka's Command and various ETB triggers in bant, Fiery Impulse and other burn, Ultimate Price and 2-3 others in B/w control.. There's lots. So not only can I use it to bounce a creature and get it's ETB trigger again, I can also boost my guys to make them more dangerous AND I can dodge targeted removal. It can effectively be a 1CMC counterspell. Imo, it's not only a great card, it's necessary in this meta for a deck using this many spirits. It's a very multi purpose tool.

The thing is, a 2/3 body with no evasion doesn't do much when everyone else has those too. So I think of it as a sorcery speed bounce. It also cannot target spells like Unsubstantiate can. The spell is probably better in the main, the creature in the SB.

I'm going to have to disagree with you on Essence Flux. It doesn't do anything that the rest of your deck doesn't do better. Selfless Spirit, Spell Queller, Rattlechains, Mausoleum Wanderer and all your counterspells already help enough with spot removal. Better to have cards that are strong in isolation than this very situational tool. If you want to run it, I think you'd do better with a 2/2 split between it and Anticipate. It's ok in smaller numbers but a playset is too many!

I rwad you're starting at EDH and asked about Geist of St Traft. I totally disagree of it being tier five. He is a beast into competitive French EDH often in 1st place. Check at mtgtop8.com. If you wanna build a Geist deck I have a nice one: St Traft Azorius Control. Youay want to check it out. And please upvote if you like it. Best regards