Good questions to consider, Daryl.
Regarding shareability, I can only speak to iOS devices. With those, you could just use the same Kindle account on all devices, and your books would be on each device. (That’s one of the nice things about an eBook- I read on my iPad, and can also get in some reading on my iPhone, in what is a surprisingly better-than-expected experience). The drawback is that you couldn’t read the same book as someone else at the same time, because the app remembers where you left off, and syncs page marker that to other devices. I’m also not sure whether Amazon’s own Kindle hardware requires you to have a unique account on each Kindle device, or whether you could share an account across multiple devices.
For something with a backlight, the only device I know of at present is the iPad, and that’s a pretty expensive choice just for an eReader.
For your library . . . nothing is going to be able to replace that. That is a nice thing about books, if you have the space.