It's unclear from your project page what your development experience is. Are you part of an existing company with experience in bluetooth printing technology?
If you are, you really should be talking about this on your project pages.
If not, you need to look this up, and say what standards you intend your device to support, e.g.
Basic Printing Profile and/or
HCRP.
If the device is intended to have a USB port, it would be brilliant to also support printing over USB, perhaps by emulating a postscript printer (since you're going to have most of a postscript interpreter anyway in the PDF display software). (Although also supporting a mass storage device mode would be good, to allow PDFs to be copied to the device.)
But for a printer replacement for proofing purposes, I really think you're going to need to think bigger than 9.7. Also, the glass substrate of an E-Ink screen of 9.7 and above is quite fragile (6" ones are bad enough). For a robust device for office use you really need to be looking as a non-glass substrate for the E-Ink display.
I think you've launched your fund-raiser too early. You need much more definite plans, and preferably some half-working prototypes.