Okay, I typed end parentheses, not emoticons. Regardless, I have several pattern designers who have me edit their patterns for language, content, and math.
The way to figure out exactly how much fabric you have and what you need from the background fabric is to first list all the pieces you will need to cut from the background fabric by size and number.
For example, if you need 22 (4-1/2") squares and 33 (2-1/2") squares. Then draw up a cutting diagram - You can get 8 (4-1/2") squares from one strip 4-1/2" x WOF. Therefore, you need three 4-1/2" x WOF strips for these blocks and will have a piece 9" x 4-1/2" leftover. You can get 16 (2-1/2") squares from a 2-1/2" x WOF strip. You can get 32 from two strips and one from the 9 x 4-1/2 leftover.
If you want to use both fabrics, it would be fairly simple. You would need to figure out the placement of the fabrics in each block. I personally would use the lighter background fabric for the center of the blocks and the darker background for the outer section of the blocks. Would really have to see the blocks to decide. The lighter fabric in the center would make the center stand out more.