Grit to use will get ten opinions from six people.
Some use a 46. I was originally told by a professional turner to use only 80.
Recently, I got the same grinder you have and started using the 120 and have no intention of using anything else.
With your set up, I would put the 120 back on and replace the 60 with the diamond.
You need only one to sharpen. If the diamond is very fine, maybe you can hone with it. Do what works best for you.
"Folks is funny critters."
Think for yourselves and let others enjoy the privilege to do so, too. ~Voltaire