If your images are packed fairly tight, you may see a speed increase by having one large raster vs individual items.
You can just leave one hidden. Or keep a test file. A minor inconvenience at the most, I would think.
In material height? Yes. And that will effect placement if you are trying to place things. If you set up your layout in the design and are just hitting print, you can change the PG setting to manual, which will keep the PG settings, and then change the job focal height. But then you’re back to a ton of clicks.
I’m not endorsing the program, but this will probably do what you want… you can define a material and settings for it.