First, welcome to the neighborhood @Fujimo ! I think it would be a good idea to clean off all of the crud, first, using pure acetone. You can post photos afterwards. Chris
No acetone won't hurt metal coins. Search forums for acetone, and you'll find more than you want to know. Be sure to read precautions regarding flammability. It will dissolve many plastics. And welcome to the group. Cal
After the dip, I don't think it would be worth it to submit for grading. I don't think it would grade high enough. Chris