Yeah I'd figure out exactly what protein skimmer and pump you want and give a couple extra inches of space. You don't like refugiums, so are you going to be running a carbon and GFO
reactor? If so, then you'll need more room for pumps. Heaters for that size tank are usually long so if you have compartments make sure to have enough room to put the heater sideways. You're going to need all the filtration you can get w/ those fish so as large of a skimmer and sump you can get/afford, do it! Did you say this will be an in-wall aquarium? How big is the room that you'll be putting the tank and sump?