About half of the stuff you mentioned is capable of being done with Autoform utility.
Others could be handled differently than you propose.
• Multi-Paged or Tabbed Forms.
--- A quick modification to the Autoform utility could allow you to generate
the tabs similar to the backend.
• Email option.
--- A quick modification to the Autoform utility could allow you to specify,
save as node, email, or whatever other thing you may want.
So, simply put, I think the main thing to consider is modification of the
Autoform to allow more control over the processing of forms.
Case
• 2007/2008 MVP • 2008/2009 MVP • Core Developer • Certified Professional Level I & II •