Can I pick up an oversized Item that is already paid for after customer service closes?

No

99.9% of the time the answer is no. However, since you have a manager friend, you may be able to talk your friend into letting you do it. Let us know how it goes!

It's faster to buy your items there and go through the checkout when customer service is open. If it's closed, they will send you away

Not at all

I don't know. You could probably contact the manager on duty at the time.