For what you're doing.... just do it how it sounds good.

1 All interfaces are digital... and theoretically sound the same. The only difference is in the audio player. Digital is digital
2 see #1
3 See #1


Personally yes, I would ALWAYS use a good interface no matter what you are using it for. Ease of use and low latency come to mind.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.