Few thoughts that will hopefully get you on the right track:
I do not think that a full implementation of TinyMCE in the frontend is necessary, give the user a textbox or something, if you want WYSIWYG, style that text box as such. Something as basic as answering interview questions can be handled without the overhead of TinyMCE
You can write your own script to allow logged in users (or any users, really) to post to your site. wp_insert_post() will help you get where you’re going on that front.
In regards to creating a profile after answering questions: you can allow anyone to answer, store the data as a cookie if they’re not logged in and redirect to the login form (which also allows registration) and then redirect back out (after login/registration) to the final processing form (can all be done from one page, fwiw). If they are logged in, data would get submitted directly.
If you do this right, you will give the user a nice interface to interact with your site through, allow yourself control over the content, keep the users out of the backend (unless they wanna be there), and provide maximal convenience for your users.