No, you're right. The EC-limit is back in place if you return to silver and haven't purchased the unlock from the c-store.
BUT: You get to keep the EC you earned during your time as a gold member, it doesn't get deleted. You just can't earn more until you drop back below 10.000.000.
I counted up the Zen it would cost to buy all the stuff that came with a 1-month gold membership a while ago and I came to about 13.500 Zen for the basic 3 free characters, with an additional 9.000 Zen just for Retrain tokens if you happened to level all three of those while being "Gold".
I was reading somewhere that it's worth subscribing for just one month and then cancelling. My question is, what do you get?
I read somewhere it's extra bank space and a new character slot?
But since I've already unlocked extra character slots with zen, would I still get another?
Yes, one month is worth it. I had four alts. I purchased an old boxed game off Amazon for $13. All the alts were instantly upgraded to all the inventory/banking rewards as if they had permanent gold status. I did gain one additional alt but I didn't use it so at the end of the month the slot disappeared.
I also got 500 Zen but its bound to STO. Since doffs are maxed out at 400, I haven't found anything to spend it on yet.