I haven't used hornworms yet because my cham is too small, but they seem solid. Mix them into your rotation, i'm sure there wouldn't be any problem with that. I have heard crazy stories of them biting though, not sure how real of a threat it is though
For gutload i use bug buffet from nick barta and organic fruits and veggies that my girlfriend luckily buys lol. Kale, romaine, sweet potatoes, mango, orange, apple, carrots, cabbage, kelp powder... I just give a little bit of each every couple days and it seems to work out. I save my fruit skins and random junk even and throw it in. I also notice the food seems to dehydrate and harden rather than mold. I keep cleaner beetles with the roaches which have helped make everything easy.