So, my friend has been playing on a Silver account all the way up to Captain, and now he's considering subscribing. If he did, would he retroactively receive the bonus inventory slots for previous promotions? That's a big tipping point for whether or not he should subscribe.

Inventory and bank slots yes. Respec tokens no.

And these inventory slots would remain if he downgraded back to silver, correct?

Yes, he would keep them if he downgrades. But you do not get to keep the EC cap increase if you downgrade.

I lost millions of EC when I went to silver because of this. make sure if he does decide to downgrade he doesn't have all his credits on one toon.

Or in your fancy new account bank you get access to with gold now. Alternativly you could buy the ec cap increase (worth it) for a pittance of dilithium traded in for zen.

On the additional 'mixed' character slot you get from a 'Gold' subscription, when you become 'Silver', you only keep the mixed slot as long as it remains 'occupied'. The moment you have a empty mixed slot, (which includes additional mixed slots purchased from the Z-Store), the mixed slot will be removed to match your 'Silver' account properties...

No... that isn't correct.

Yes it is correct.

A gold player gets three slots and a silver gets 2 slots.

If a player creates a character when they are gold in the third slot they get to keep it even though their free slot count is currently at -1.

If they delete a character they will have no free slots remaining as a silver player is only entitled to 2 slots. ie -1 + 1 = 0

If they do not delete the character and buy 2 slots from the store they will receive 1 slot they can use as the other one is preused from when they were Gold. ie -1 + 2 = 1

Then mine was bugged bcause I have not purchased any additional slots and have 3 FED and one KDF and am able to delete a character and make a new one.