1) In the server behaviors panel, click the "Server Validation" server behavior. Select Required Not Blank validation type, then click the lightning bolt next to server variable and select the form element that should be required.
2) you can set the default checked state in the property inspector. Select the radio button that should be checked by default and in the property inspector, set the checked state.
to get the text field to show or hide, use the client side validation show hide layer behavior.
select the no radio button, then in the behaviors panel, click the plus button and select WA Validation toolkit -> Show hide layer
3) This is done using the Required not blank validation again, this time apply it to the check boxes.
4) Server validations creates a validated entries binding group on the bindings panel.
Set each form elements initial value to the corresponding binding from the validated entries binding group.