Ya, I am planoing to get some door trim on it also. still wana cut out the holes a little more for easy access to the hooks so I dont have to struggle putting them on or off. I got the hooks from Harbor Freight.
I would also make a plate that goes between the frame and bolt heads. 3/16 should be sufficient. Then put in some grade 8 bolts and at least the mounting will be very secure. The strength of the tow hook is then subject to whatever quality of metal the company made it out of. Should be good for most use, but just be careful of any sort of sideways pull or when winching. I like how you made them come through the bumper, looks nice.
Yes please get some Grade 8 bolts. As for the plate suggestion, I wouldn't worry about it. The frame horns are stronger than you think and will hold out a heck of a lot longer than the hook will. I have had 10,000 Lb+ applied to both of my hooks and neither the frame or hook ever moved.