Hi Bill,
Support for a specific Email question type and support for limiting authenticated users to one form are both items in my project tracker for future enhancements of Form Wizard Pro, so at some point those items are coming.
Which captcha are you using? Recaptcha is not supported in Form Wizard (I couldn't get it to work correctly there) even if it is set as the default captcha in Site Settings, so it should be falling back to Subkismet for the form wizard captcha.
I'm certainly not aware of any 10 second timeout for the captcha. If the app pool is recycling while the user is filling out the form that could invalidate the cache and the captcha. I would look in the Administration > System Log for any evidence that the application is recycling too frequently, it would be logged as application start and application end events. If you see those happening a lot it is most likely caused by hosting in a low memory environment where they forcefully recycle the app pool when a certain amount of memory is used, if the memory limit where it does that is too low it will cause frequent recycling and it will kill performance of your site in addition to causing problems like the captcha becoming invalid too often.
Hope that helps,
Joe