We would not want to hold any BTC; just offer it as a convenience to customers.
I read on one post that there's a 25% exchange fee. Is this correct?
That's totally up to you if you wants to hold or not you can withdraw at any time like end of the day whatever and regarding pricing you have follow their different plans.,
My suggestion is just go through their web links they both have "How it works" section you'll gain more info from that.
https://bitpay.com/pricinghttps://coinbase.com/docs/merchant_tools/payouts