yet another page size quandary

I am building a cruising guide for boaters, with fixed layout, and want it to be a size that is viewable on most any device or computer screen.

I accept that a pixel is a pixel and that I would be best to target the 768 x 1024-pixel ipad screen size. My concern is the readability of tiny text in illustrations.

I create maps in Illustrator, in some cases using text as small as six point, just large enough to be read at 100 percent. In different devices, the resolution might be the same, but the size is not.

To confuse the issue, when I save a 768 x 1024-pixel document as a pdf in Indesign, it is much larger than an ipad screen. What is the real size?

Is there a way to ensure tiny text in illustrations can be read by users of all devices, or should I just remove all tiny text?