I have a bunch of the same items and I was wondering if I can put a bunch in my machine at once and engrave them all?
Yes but trickier than doing one and ruining one is cheaper than ruining a dozen.
No there is no problem with making mutable of the same item. You will just need to copy and paste them either in your design or in the glowforge ctrl + c then ctrl + v as many time as you want.
If you want to reduce print time, you need to combine your graphic outside of the UI, not copy and paste inside it. Otherwise, it will only print individual copies, not one large set together.
I do 1-1/2" tokens engraved both sides, and all I can get in at one time is 77.
I find it much easier to prepare the file in Inkscape as efly said.