Hello, this is my first time here and was looking around for Global Entry information and it seems that this forum has a wealth of information.

I will be travelling out of US in the end of December.
I will be leaving through IAD and coming back through ORD.
The closest global entry location is CLT.
I am not a US citizen but I recently obtained a green card.

Now, here's my questions.
1. I applied for Global Entry, got the conditional approval, and voila - no interview slots. How often are interview slots available? I've heard here check every single day..
2. I only have 1 hour layover in IAD and it's going out of country so it's unlikely for walk in anyway. For ORD, I have a 4 hour layover. Is it best to just go for walk in interview in ORD? Should I schedule?
3. I already have conditional approval, which means I paid for the application already. Do I need to pay again for the walk in interview? Will they have my data already because I'm conditionally approved?
4. Do I need any fancy documents for the walk in interview?
5. For walk in interview, is it before or after immigration?

Thank you!