Why so insistant with gravel? Listen, you have to have sand in your system, but no one said it had to be in your tank. I run all my reefs bare bottom so I use remote sand beds. Put a dsb in your sump or in a secoondary sump and only drain a quater of your water over it. I can get you photo's if you'ld like.
Sure you can. My local PetCo uses gravel because it is easy to keep cleen. Granted they have a massive protein skimmer and also a really big sump in the back room full of fine crushed corral and live rock.
One thing you have to keep in mind is that you greatly reduce the biological presence in the tank with gravel. You might want to look into a good protein skimmer with that fat boys you're going to put in there.
PetCo knows less about keeping fish al;ive than my cat. Don't take any ques from the major chain stores.
There is a chain store here called Pet Extreme, and one day I was in there buying cat food and decided to take stroll through the saltwater section and noticed a sickly looking Madarin Goby. I decided to test them asked homeboy what this fish eats, and his response was literally, "we don't really know. We just try to sell them befor they die." Now that's service with a smile.