Re: What does it take?
I have a horrible track record of underestimating projects, and I can tell you that I wouldn't touch it for less than $100K -- and that's with zero coordination or communication costs, where the architect, designer and implementer are all on the same page all of the time (because they're the same guy). And you'd be nuts to hire one guy, but you can't hire four and make the project go four times faster -- it might cut the time in half.
There's a lot to do, from researching the APIs for the various institutions you want to deal with, to "simply" building the application, to hardening and testing (and the test/debug cycle will be at least three times the length of the architecture and coding cycles combined before you're ready to call it a "minimum viable product" and move to a public beta). Then there's the cost of running the site -- you need physical security of the servers (that means co-location of machines you own in at least two separate "hardened" data centers), redundancy in your redundancy, off-site disaster recovery, et cetera, et cetera.
You're probably looking at nearly half a million spent before you're able to buy a packet of instant ramen noodles with the first profits from the venture. There's a potential for a vast income, yes, but it depends on making a big bet up front. If you were a fanatical coder with a dream and the know-how, you could place a significant portion of that bet using sweat equity, but you won't find a "technical cofounder" to execute your idea on speculation. This isn't an iPhone app, it's a serious enterprise-level, security-is-paramount, legal-liabilities-attached software project that just happens to have a web front-end.
That being said, if you're up for the hundred grand, let's talk, and I'll show you how I'd earn every penny.
“Beware of bugs in the above code; I have only proved it correct, not tried it.” --Donald Knuth
"It was as if its architects were given a perfectly good hammer and gleefully replied, 'neat! With this hammer, we can build a tool that can pound in nails.'" -- Alex Papadimoulis (on TheDailyWTF.com)