To clarify the legal side, according the ATF if you are going to have a business that merely modifies the appearance of a firearm (engraving, camouflaging, painting, etc.) you should still be a licensed gunsmith to avoid running afoul of their rules. This primarily has to do with making sure you are not modifying serial numbers.
The ATF ruling in question: https://www.atf.gov/file/55461/download
I think Will has pointed you in the right direction. I would also be very careful with where Create sets your zero. On flat surfaces like slides, I would think the engraving would go well, provided you shim the slide so that the surface you are engraving is perfectly level with the X-Y plane of your machine. If not, you will get uneven surface depths. I'm not sure how you would engrave on a curved surface like grips to account for variation in Z height, at least not in Create. You may have to switch to a more advanced CAM program for that. I'm a firearms enthusiast though, and I look forward to seeing your work.