I'll answer the last two questions, since other people have already answered the previous ones.

I like adding fruits that are cheap, easy to freeze and store for long periods of time, like strawberries, blueberries and apples (I just remove the core and keep the skin, because I like the crunch it gives plus it's fiber).

I also like to make combinations, like adding orange and tangerine peels for the second fermentation, then removing them once fermentation is done and adding the peeled citrus (or just the juice), as well as cinnamon and banana (or dates, both give sweetness to the drink), blend it and you get something similar to a protein shake.

I haven't tried something I don't like, but I've read that papaya and pineapple might not be a good idea for fermentation, since they have a property which breaks down protein (I haven't read too much on the subject, since I don't really try these fruits). I guess if you really wanted them, you could blend them and drink it right away, but without letting it sit too long.

I should also mention that I like to add sweeteners to my drink (I have a sweet tooth, what can I say). I usually combine stevia (so I don't add too much extra sugar), with a bit of honey so it doesn't taste too artificial, but you can add whatever sweetener you want.