We love our valentini and like dougai, we have had ours about a month. He is in a 55 gallon with a pair of percs, yellow watchman goby, yellow tang, various crabs and snails, fire shrimp, cleaner shrimp, and an urchin. There were some territorial things with the tang the first few days but since then all is well. The tang and the valentini, or Mr. Puff as he is known to our kids, hang out together all the time now. They like meaty food and need to be fed things which will help them wear down their teeth. From what I have read, they need a minimum of 30 gallons and can be aggressive to inverts but haven't noticed anything as of yet. One person suggested, get your inverts first (shrimp and such) and then add the valentini and they may see the inverts as part of their home and not food. But adding them after, they may just think you are feeding them a tasty treat.
I have no clue if that is accurate but just a thought to ponder.... :notsure: Anyways, hope you are able to get him and enjoy 'cause they are very cool fish full of personality.