Aaleigha, ok we'll try not to cause an international incident :lol: . My reasons for washing my fabrics are the two biggies you've already mentioned, I have had fabric bleed in a quilt and trust me you only let this happen to yourself once :cry: , also as I understand it fabric can contain other chemical residue used in the manufactoring process, and another thing prewashing does is to help show up any flaws that there might be in the fabric.
Others like their fabric not washed as leaving the dressing in the fabric makes it easier to work with i.e. holds it's shape better
Re Amount of Fabric for Next Month
You only need a small amount, a fat quarter of light and a fat eighth of the dark will be more than enough. You will have leftovers, but having a bit too much is better than not having enough :P