Conditional Form Elements

I am creating a registration form that is being input into a database. This is a long form that will include inputting into relational tables. The database has an enum "payBy" column with the options: 'check', 'credit card', 'paypal', 'no charge' in the main table.

I would like part of the form to be conditional. I have a repeated dynamic checkbox that is being created from another table (needed in order to do the manage relational table behavior) There are 9 options where I would like 6 of them to bring up a radio group or checkbox group that they can select to pay by check, credit card, or paypal (this will be inputted into the payBy column in the main table). The other 3 check boxes, I would like to have the option to input "no charge" either by a hidden field or by a check box that is pre-selected (also inputted into the payBy column in the main table).

What would be the best way to approach this with the validation toolkit? Much of the form will be validated client and server side.

Thank you in advance,
Christina