I've used MDF for years in car audio and know how to work with it, but I've read lots against it, so may go for ply. I found birch ply harder to cut than MDF with the jigsaw, but I'm hardly doing any cutting, so will probably just go for Ply.
Not worried about dirty stuff in MDF, most of the stories are chinese whispers and hold no truth. The dust also doesn't really affect me apart from the joy of lots of bogies at the end of the day. lol