I'm afraid you can't set the form submitted values in the MLS form. That's because the mls form is not on your site, you simply display it in an Iframe in your page. It would be quite possible if the code was on your site.
Yes, you can use it as signup form, and ABVFP can autocreate the necessary database table to store the info (plus IP address and Date of submission, which are standard with ABVFP). However, you will need a database interface to browse, sort, view, edit delete, and finally, EXPORT in csv or excel file the database listings. If you are interested in such an interface,
contact me.