That's a really big lawn!
If you want to just get rid of the moss you'd be better off buying soluble iron, the fertilizer you linked to doesn't contain any iron which is what you need to get rid of moss.
You can buy fertilizer with added iron, just look for +fe on the label.
I use pitchcare.com for all my lawn products which I find cheaper, this is the soluble iron from there, it works out you'll use very roughly £2.50 to treat your full lawn.
http://www.pitchcare.com/shop/soluble-turf-fertiliser/maxwell-bullet-soluble-iron-20kg-bag.html
If you do want to start putting fertilizer down, with the size of lawn you have it's going to start costing you a fair amount of money.