you may want to run a zigzag stitch around the edge before washing it, fleece can fray on the edge, just like minkee (which is also a fleece)
why are you going to wash it first? it does not shrink, the colors do not bleed, and unless it is very very thin i would think there would be no reason to wash it before using it, you will want to wash the other fabrics because ... polyester doesn't shrink but cottons do; but if you use them together when they get washed they fluff and get really really soft.