Is it possible to prepare a (large) batch of roux and then freeze it, or will the texture and flavour be destroyed in the process? 
You can freeze roux and store it up to 6 months without any problems. I put them in plastic ice-tray forms until they are frozen, then move them to a refrigerator bag.  Just keep following things in mind:   Leave a bit of room in the container before putting it in the freezer - roux expands when freezing. Bring it to room temperature before using it.  