you will not need an overlocker if you are happy to have regular, folded over hems -- you can just straight stitch or zigzag a hem all around the edge of the fabric.

With the flanelette wraps, you could even sew two fieces of fabric together and have it double sided.

I would make them at least 100 x 100, especially the muslin wraps, otherwise you baby will outgrow them super fast!

So make sure the fabric is at least 100cm wide (i think for narrower fabrics 112 is standard, so this would be fine)