Puffer would have to go as well. It will get to big for a 75 and they are not reef safe. To add on to what Trigger40 said "maybe the angel" cause some will pick at coral. I usually go with it's not if they will but when will they pick at coral.
Since I got them on Wednesday I've only saw one or the other. Just fast little glimpses. Last night I,finally got a shot of both of them. I now know their hiding spot, so whenever I go to check out the tank I can usually see them.
Ya they are usually spotted within inches of each other. They were at opposite sides of the tank when they were first introduced to the tank but now they are always together.
Some would say yes, some would say no. I've had a few in the past all of mine were pretty mellow when it came to others but can throw down if need be. And my answer was pretty much no help lol.
Honestly a tank for a coral catshark that has a foot print smaller than 8 feet by 3 feet wouldn't be good for it long term. They are active swimmers at night.