IMO, the #1 thing for you to do (for arranger) is learn how to play chords with your left hand. Study basic music theory as to how chords are comprised so that you can figure this out for yourself. Start with majors and minors and then get into more complex chords. It won't take long. I was amazed how far I advanced in my first two weeks.

Generally, you change your variations at the beginning of a new verse or at the chorus. Sometimes, I never change the variation, as the others don't fit. You'd rather not do that because you would rather have some VARIATION, haha. You can add variation with changing a voice or layering.

If you have a decent ear, with practice, practice and more practice, you should be able to figure out most songs on your own without chord charts. I said, MOST.

As for lyrics, do this...

google "lyric (song name)."

For chords,

google "chords (song name)."

You can also google both and sometimes find them both.

Some chord charts you find are totally wrong. Hopefully, your ear will tell you when something is not right.