For the conditional question you can achieve this using CSS Form Builder's client validations. It is the show/hide client validation that will allow you to do this. If you are not familiar with using the client side validations then the help is a good place to start.
The idea is that you would have a validation applied to the select list for required. Next you would put in the response validation of hide/show and select the select list as the trigger and the field you want to hide or show as the target. You would then go about applying the rest of the client side validations like normal. I'm including a example page for this type of client validation. It uses a checkbox to hide or show the next part of the form.
As for putting the form on multiple pages you can do this by having the first form page post to the next. Then on the second form page you would add in hidden form elements for each field on the first form. You would then go to the bindings panel to set the value of these hidden form elements to the posted values from the first form. This way when you post this second form it will contain all of the info from the first one as well.