I'm doing a similar project, where I take an old laptop screen (not touchscreen unfortunately, but free) and turn it into an e-reader, you can check out some of the things I'm trying for reference over here.
From what I can tell there are 3 main hurdles
1) A case for it all. I'm making mine out of clear acrylic, but my main problem is I don't want it to look boxy.
2) Charging power supply. Check the chip I'm using to control it. It's a cheaper one that can only charge AA type batteries. They arrived in the mail today and it turns out they're REALLY small!
3) Screen attachment to R-pi. This is a really big one. If the r-pi team decides to keep the LVDS interface then we can directly attach to the r-pi and save a TON of money. If they don't, however, you'll need to drop about $30 to get a LCD controller card that matches your touchscreen LCD.
Dear forum: Play nice