If your panel buss and breakers are rated for 75 degree C and the grounding buss is bonded to the metal enclousure and the neutral buss is "floating" (not bonded to the enclosure then it sounds like you are going to be code compliant. The grounding electrode needs to go to the grounding buss and the panel must have a main and the neutral must be full size based on what you said about the load. The grounding electrode conductor minimum #8 but most installers will run #6 because it can be installed without being in conduit. No concern about harmonics. Single point grounding is another topic all together and what you are doing is just plain old grounding.
