Looking to develop a high-scale "Co-Registration" path system similar to that of Zeeto.io (Zeeto Media)'s solution which can be seen here: https://i.getitfree.us/splash.html
A user registers by filling out a short form (basic contact details) which takes them to a "full form" (full contact details and mailing address, gender, age, etc.), then takes them to a range of survey questions to build a profile (that we can later segment for marketing purposes).
During the survey questions (and based on their responses), they will be shown a number of paid offers that they can "opt in to" by clicking "Yes/No" - walk through the full "path" on https://i.getitfree.us/splash.html and you'll see exactly what is meant. These offers will be posted via API to different buyers/advertisers (who will be managed by the the admin interface)
System needs to capture new user profiles and dynamically populate a range of survey questions (which can be configured via admin interface). Most importantly, MUST be scalable to hundreds of thousands of registrations per day, and generally maintainable (written using best practices and proper design patters, OOP, and up-to-date development flow). (obviously we'll need to add/scale server and network resources as it goes, but the system should be built to easily scale up/down as needed)
Open to whatever cutting-edge stack is going to work best for high-scale and easy maintenance. Please explain your high-level reasoning behind the stack you plan to use in your cover letter.