Hello and welcome!
Your question is difficult, because you have so many specific needs. One thing, I don't know how much an iRiver Cover Story costs, so I don't know whether the devices I know about will be more or less expensive than that.
I know a bit about the Sony Daily Edition and about the enTourage eDGe, either one of which might suit your purposes. I'm not sure because I don't use mine the way you will be using yours. The Sony has a 7" screen, so possibly too small. The full-sized eDGe has 2 screens: a 10.1" Android tablet and a 9.7" e-ink. So the size is right. Both devices have memory card capability. Both will work with Word documents, but I can't remember off-hand whether the Sony reads them natively. The eDGe comes with Docs-to-Go, which reads Word documents on the LCD side. I
think (but don't quote me) that they both can display jpg and png files.
Anyway, it's a place to start!
Good luck in your researching!
Check here for more info on the above:
https://www.mobileread.com/forums/forumdisplay.php?f=100 (Sony)
https://www.mobileread.com/forums/forumdisplay.php?f=218 (enTourage eDGe)