I changed my oil in my 04 when the DIC told me. It was def over 5000 miles per change on dino oil. The Z06 uses Mobil 1 and the DIC usually goes 8500 miles between changes.
I would save your money on the octane booster. It really doesn't work.
You also don't really need to Seafoam it. Maybe ever couple of years its worth it but I wouldn't be doing it on a regular basis.
2003 Corvette Z06 - MGW shifter, Corsa X pipe, Corsa Xtreme exhaust, Texas Speed long tubes w/o cats, PowerStop rotors/pads, Conti DWS tires, C6Z51 F&R sways, C5R headlights, tuned
04 GTO - sold