I downloaded GIMP tonight and used it for the first time. My first etched photo is about 1/3 of the way through and so far looks fantastic. Took me about an hour of watching the video on youtube and doing the same thing, then going back and doing a bit more to my liking.
Doing it on draft board. As its etched not cut, should I have removed the backing paper first? (bit late now, but be good to know for next time)
You don’t have to remove it and it keeps the etching “cleaner”, but you may lose some of the fine details if you leave it on. (The light lines will look good on the masking, but sometimes they don’t make it all the way through to the material.) It can also be a pain to remove the masking on some intricate engravings, Personally, I tend to take it off and just up the power a little bit or slow the speed. After you do it for a while you’ll kinda get an intuitive feel for when to remove it and when to leave it. 
Alcohol hand cleaner does wonders for that