Since the iPad will automatically 'downsize' your larger photos, then reducing each to the size mentioned in your post (i.e. 5" x 7") may not be necessary - all that I can say is try to make a few 'smaller' and give it a try - no promises here. Also, keep in mind that the chart I posted is more important in understanding pixel size when printing out images - the 300 ppi translates to 300 dpi which is a standard for printing images w/ good resolution (of course requires a LOT more pixels); however, the pixel density needed on a computer monitor is much less (72 ppi is often used although the iPad w/ retina display portrays at a much higher pixel number).
My bottom line - first, 'Restart' or 'Reset' your iPad just to see if that makes a difference; second, downsize a handful of your images & put them on the iPad just to see if the change in size helps; and finally, don't use your iPad as the main 'storage location' for you high pixel density photos - you may want to print some out at sizes larger that just 5" x 7" (e.g. I print out some of my travel photos at 8" x 10" and then make my own frames - my digital camera takes images up to 14 MP - usually a 5 MP+ size reduction gives me a nice photo). Please post back your results and if you still have questions, then ask away - this stuff is really confusing! Dave