ecookbooks vary a lot in terms of how best to use them. Some have very useful tables of contents and indexes that link directly to recipes. Others are not as thoughtfully edited. If the ecookbook is indexed here on EYB, looking up the recipe on the EYB website and then doing a search on your Kindle can work when indexes and tables of contents do not.
Having said that, my favorite way to use ecookbooks is with the free Kindle app on my iPad. (I believe there's also an app for Android tablets.) That way I can see all the color pictures in color, and the screen is larger on my iPad than on my Kindle. Oh, yes, there is also a free Kindle application that runs under Windows. Not sure about Macs, but I would guess there's one for them too. You can have copies of the same book on as many devices as are registered to you without paying anything extra.
About the cloud, Amazon takes care of all of that for you. Whether you use a Kindle or a Kindle app, it checks in with Amazon to see what you've purchased. You can always double check by telling it ti Sync. If you want to read something that is not on your device, it is automatically downloaded. If you need to make room, you can archive it.
I hope this helps. These days, almost all of my cookbook purchases are digital.