Should I be worried about Moss / Algae / Mold on siding?

[Henry Holt]

I am considering purchasing a single family house as a buy and hold investment.  The property has about 3 feet of moss / algae / mold growing on the siding.  

Is this something I should be concerned about?

What remediation would you recommend?

Is algae growing on the side of a house indicative of mold being inside the outer wall as well?

Any thoughts on how to best analyze this situation would be really great!  Thanks!