HELP... multi-step trigger-based forms with auto population

HELP... multi-step trigger-based forms with auto population

I recruit potential vendors for my company through a form on my website. The challenge is that the large amount of info we require (often 50-60 data fields) often leads vendors to submit an incomplete applications or abandon their application entirely.  In an effort to minimize incomplete vendor applications and abandonments, I'd like to make application submission less non-intimidating and more authentic.  

Let's say I have 50 pieces of information I need to collect from potential vendors. Here's how I would like it to work:
  1. Potential vendors complete a form containing the first 10 data fields (we present it as a preliminary application)
  2. About an hour later they receive an automated email saying somethings like, "Thanks for applying. We reviewed your preliminary application and would explore working with you further. Click here to provide more details about your company..." 
  3. The vendor clicks the link and is led back to a form where the information they provided previously has been auto-populated, but they now are presented with the additional fields they did not see the first time and are asked to complete that information.
  4. The vendor receives another email verifying their application has been received and we will contact them once we have validated their information.
My question is... What is the BEST way for me to accomplish this?