As I know, you can only develop them using the macOS operating system, or by running it on a virtual machine, maybe, not sure about the second one though, don't know if someone is doing so, but theoretically it should work. You could ask an iOS developer https://www.cubycode.com from cubycode, they are doing a lot of cool apps and I am sure that they can give you more information about this one, and help you to solve this problem. I am sure that there is a way to make it even if are not using macOS, there should be some kind of program to avoid this.

Yes you can!
Read this tutorial

However, you should probably use mac for the best experience.

You can't develop them here, you have to use Apple's official developer tools (Xcode).

Yes, you probably can. I am not sure though.

Yes, using swift you can develop them, i think here too.