Downpayment is generally 20% but they could ask you for 30% if yur credit scores look sketchy. Remember tho, they will include any discount from Magical Beginnings in you downpayment, so if you take the $10 off per point (offered thru the end of the month), they apply that to your downpayment, so you could end nup with a 10% downpayment under these circumstances.
And no, there is no pre-payment penalty, which is great for getting Disney Rewards on the Disney Visa.
Good luck!