Backup Large amounts of Data

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I will do the initial backup at home, so my incremental backups should not interrupt his network much at all.

What kind of bandwidth does he have? Likewise bandwidth caps. Earlier you stated

I am adding about 100-300 gb per month

That means 100-300 GB per month coming down the pipe at his end and up on yours. Unless you are incrementally going to mail HDDs each month I don't see how that gets you to "low bandwidth interrupt" unless "home internet" is pretty generous.

I know Crashplan offers a free software for specifically this.