Kindle to Ipad questions

[IndyMLVC]

So I'm thinking of moving over from a kindle to an ipad.

The kindle that I have is great. In fact, it's practically the last great kindle that Amazon produced. The specs from every single model since haven't matched up, unfortunately. I kept waiting for them to produce an updated model but they just haven't.
https://www.theverge.com/2017/5/16/1...s-hdx-7-screen

Although it still works extremely well, it's very much lacking in app support at this point. There are lots that won't update or aren't available for my model any longer. It's essentially becoming an e-reader and I would like to be able to update my firefox browser.

Thus, I'm thinking of switching over to an ipad. Because I have an iphone, I figured it would be an easy transition. However, I have two pretty major questions:

1) Am I able to sideload books like i can on my Kindle? I have a lot that are in my library already - some are from amazon (yes, I know there's a kindle app) and some are *ahem* not from amazon. Will I still be able to organize those with itunes?

2) how does it work when you have both an ipad and a phone connected through itunes? How does it know which to sync properly?

3) can you sideload movies that are in mp4 format as well? I have movies like the Star Wars trilogy that I'd like to keep on there.

If you have any other thoughts and suggestions, I'm open to hearing them! Thanks!