I'm building a Cloud Platform, and the next phase of design involves building an extensible BaaS back end. (see http://youtu.be/lNi-05-PyEw)

The reason I think we can attempt this, is there are dozens of these kinds of extensible back end data proxy's popping up almost daily at this point, which tells me the enabling technology is there to build one from scratch in a few months.

I'd like to start in the right area:

What kind of Dev background should I look for?

What kind of tech stack should I build on?

What kind of costs can I expect in terms of man-hours, etc...

I know there isn't one right answer here, but I think this is the right sub to post this in, and credit will go towards to most constructive answer.