Hi list3ner,
So there's two good options right now (that I'm aware of) with Android export, Crosswalk or Cocoonjs. I prefer Cocoonjs (performance usually seems better and it has support for things like ad networks and in-app purchases)
So for CocoonJS
1. sound works fine, check out some examples of what other people have done here: scirra.com/forum/c2-games-on-google-play-android-market_topic60466_page12.html
2. Performance is usually pretty good if you build your project right (read scirra.com/blog/112/remember-not-to-waste-your-memory)
You may run into some issues when compiling to mobile so you should test often (use the the CocoonJS app to launch your test your app quickly over wifi, read the section titled Testing with the CocoonJS launcher scirra.com/tutorials/303/how-to-export-to-cocoonjs)
3. Yes with CocoonJS it compiles it to an apk or xcode project for you
4. Construct 2 is my favorite game engine--I'd suggest you download the the free version and try it out and see if it's good for you. There's great documentation, samples, community support, and tutorials to look at.