RE: Writing all over maps. I feel its much easier to have something permanent when youre in the plane as you dont want to risk rubbing off some important information. I use permanent fine pens - black for my route, green for the 10 degree lines and red for wind. I keep the blue one in the plane for any diversions / changes i need to make in the air.
To take it off just buy a cheap bottle of nail polish remover and it comes off very easily.