im going to install my speaker this weekend, and need to know when making the baffle for the speakers, how think mdf do i use, would 9 suffice or should i go 12mm with another spacer on top, any other tips you guys could give, and is it neccessary to treat the mdf, and what can i use to treat it.

depends on the size really.

9mm should be thick enough, just paint it with a thick coat of spraypaint, it'll soak in, so make sure its thick, this would of course be after you've cut out the speaker hole, mounted the speaker (and removed it again) and test fitted it in the car.

so any basic spray paint will be fine.

lots of it, yes.

12mm would be better when it comes to mounting the speaker in the baffle.

Some paints won't dry properly on MDF and stay tacky. Ask someone when you buy the paint. You just need to seal it so it doesn't get waterlogged.
9mm or 12mm should be OK, but check the depth of your speakers for window clearance and also check how much room you have behind the door trim. One thickness might work out better than the other.