Probably best to ignore both git and node_modules folders with arq. Arq goes back and validates old backups sometimes (this makes my fans spin up much more than actually backing up weirdly) and both of those folders are going to be scanned and revalidated after the initial backup.

Fun fact, rumor on the webs is that a new Arq version is in the works! (Look at their twitter feed for screenshots they sent somebody recently)