scaling in LAzyCam

My ignorance is going to shine thru, but I bot a minimill for my science/tech club kids and they know more than I. But they (we) are having some problems scaling stuff in LazyCAM. I think most of what we have done has been Corel or JPG thru LazyCAM to MACH3 to the minimill. So is there some way to check dimensions before cutting?

And we are about to do a dxf that should have appropriate dimensions in the dxf. This should be straight forward, right? or is there a scaling option here too? And do we set the tool size in MACH or prior?

Thanks, Chuck