Jim answered the questions well.

My Focusrite has a button on the input of each channel that lets me choose line level or instrument level.

One bit of advice regardless of anything else..... ALWAYS turn the level control DOWN to zero on the channel when you plug something else in. Then, you turn it up as needed. You probably know that but it's amazing how easy it is to forget that and end up damaging something because the new source was overloading the input.

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.