Looks like VLC falls back on software decoding instead of using the hardware decoder which explains your problem. No idea why this is happening and you are the first to report the problem.
What is the audio codec? Can you do a debug log? (to do that, go to settings within VLC-iOS, enable logging, play the file, then go to the "Files" app, navigate to the "VLC" folder and see the "logs" subdirectory)
You can resize the panel by clicking in the bottom-right and dragging the panel. However, you cannot make it stretch easily across the entire width of the screen.
This dialog will appear only if your have streaming to Chromecast enabled and your Chromecast device does not support the video type you are trying to play. If you want to watch locally, it will of course just work without burning your battery.
I have no idea what you mean with looping an audio track. The "L" key is equivalent to the "b" key on Windows and Linux. It switches ("cycles") through the list of available audio tracks. Why we decided for a different key on Mac many years ago, I totally cannot remember.
hmm, sorry, but you should be using a stable release of VLCKit and not an alpha that we mainly do for internal tests where especially all the methods you mention will be completely re-written for the next alpha release.
You can send any file type using that feature but VLC will only show what it can play, so that's video and audio files, but no Word documents and no photos.