some of the descriptive listings might confuse you...you can ignore some of it sometimes.
reading the description in the product detail, it SEEMS to show
1 non lit 120 fan in back (large)
1 lit 120 in front (large)
1 lit 80 on side (medium)
Now for me I consider 120 mm to be large, 80 medium, 60 small...
There are intermediate sizes like 92, and what I consider XL as 140. There are even Jumbo 250 mm fans, but those tend to me more for show ;p
Since the case is geared toward a green color scheme, we can assume the lit led color is green. Again, assume, unless they state GREEN, which they don't. Even when I've seen case specs, they don't always deliver.
The ATX, mATX...those are the sizes or form factors of your motherboard. Usually ATX cases have mount holes to match smaller sizes. The size preference is up to you, typically a mid-full tower people will buy ATX sizes. Sometimes people like to buy mATX (micro ATX) and fit them in huge cases. Just remember the smaller you go, the less options you have, in terms of sizes of cards and number of slots.