I only have the M2 so I just use very low infill when I have to use support when printing with Petg as it is not suited for support as you know. I set my XY speed in S2D to 200 rather than the default 300mmS for non printing motion. This is where a lot of stringing happens. I also never print much faster than 50mmS if the part is not a large simple shape. Slower = less strings.

If using S3d, you may want to set your support to print 1 layer of 100% dense support this will give the PETG a smooth surface to land on and make sure your upper vertical separation is not set more than one.
Good luck!!

I never use a fan when printing with PETG

Recently I have starting using Makergear brand ABS in place or PETG if the part will not be outside or exposed to sunlight.