A quart typically covers ~ 100 sqft.  A pint per color ought to do it.  

Google image search for mountain wall mural layered to find other's works. Try to identify what it is about the ones you like that works so well.

Print out a color image of one of her large photos (maybe take the URL to Kinkos or Staples or photo store and ask them to print it to 'match'), take the print to the store, find color swatches that match.

she wrote a blog post about her process:

http://pamlostracco.blogspot.com/2014/05/mountain-mural.html

Here are time lapse videos showing a different people doing similar:

https://www.youtube.com/watch?v=iQGZi75w5LY

https://www.youtube.com/watch?v=QPE5G2SR0Zs

https://www.youtube.com/watch?v=QVQ8mPmSZS8