Our deposit was 10% of purchase price so $1,700. I sent it as a personal check but they would allow a credit card for an additional fee.
I wouldn't wait for your loan to summit an offer of you know you will be approved for your loan. The resale process take a while (I am 3 weeks in today and still have a long while to go)
Also our deposit is 100% refundable is Disney buys our contract or it falls through for any reason on the sellers behalf.