I can't help you much right now, as I'm in the process of putting custom current drivers together to power the thing and I don't have a full solution yet, but I've been working on adding a 30w diode laser cutter to my homebuilt 3d printer. If you are looking for resources, the marlin 3d printer firmware has a builtin option to run a laser engraver or milling spindle that is pretty well put together. Depending on how much of a gantry you already have set up and how much code needs to be rewritten, this can obviously become a pretty large project. I'm planning to either use fusion 360 or laserweb (
https://github.com/LaserWeb/LaserWeb4) to generate the requisite gcode. Most likely laserweb.
Your mileage will vary with laser diode based engraving, its pretty important to either have a really small spot size or overwhelming power output, as long as you get a reasonably high power density it should work fine. If you already built a laser you know what it's limits for burning things are, so I don't need to tell you that. Personally, if you want to just engrave I would go with a beam expander and focus lens setup on a singlemode diode to get minimum spot size, sacrificing depth of field, and I probably wouldn't bother building a low power cutter.
If you have any specific questions, I can try to help. There are a bunch of tutorials online for software setups like gbrl (
https://github.com/grbl/grbl/wiki) and some cheap gantry designs using old cd/dvd players for the x/y gantry.
It's a fun project, even if slightly impractical. Good luck!