Chronic do better in small packs so unless your adding 5 or more then neglect them, the tomato gets pretty large like the clarkiis do so he will eventually probably get aggressive but not sure. If there's enough rock work I'm sure the six line would be less aggressive.

Watchmen are sand bed guys so either keep him alone or get him a buddy. Love pistol shrimp so ill suggest it to anyone curious haha

I've had a coral beauty in my 28g cube but I'd stay away from him unless you have a 30g long with rock work and caves. Mine was shy and hid but could be cuz he was in a small tank.

If I'd start again... A pair of neon gobies, dotty back, blennie of some kind, hermits, snails, not sure for a 30g.. I'd probably go species with it and do a Valentini puffer or green spotted puffer.