HI,
I would like to use a form as a content gate so that when it has been filled before that info will be written to the cookie (or other method) and the form will not appear a again for the user. Instead, it will display the full page HTML without the form.
Thanks!
Use the Known Visitor HTML feature ("If Known Visitor, show Custom HTML" in Form Editor » Settings). I've written extensively about it here if you search.