Bare bottom, bioballs, fluorescent lighting (PC or vho) capable of being increased from low to high intensity in stages, sump, no live rock, no sand,
sponge filters either in tank or for the overflows, temp controller and good heaters, a skimmer is nice, but not absolutely necessary, although post formalin dips require good aeration for the vertebrates. A media bag for carbon is useful as well. If you really want to go high-tech, a reactor for some Phosban would be good.
If you use the bioballs, make sure to keep water in the tank running all the time, or keep the bioballs in the sump of your main system (this is to keep the bacteria alive for denitrification). Nitrate levels in such a system are not an issue, you can change the water to get rid of it, but carrying pathogens back to the main tank is an issue.
Bioballs allow for short-term ramp up of mineralization of ammonia and nitrite while allowing for sterilization of the media after use (Clorox) without ruining the rock or sand.
Lighting otion is to allow for smooth increases in photoperiod and lighting without bleaching
coral specimens
No sand and rock for obvious reasons.
Sump for larger water volume and good circulation.
Sponges may be sterilized after use, but need to be kept with several spares in an area where they can keep colonies of bacteria seeded to the sponge and alive for mineralization of ammonia as well as the bioballs.
Heaters and a good controller allow for high temps or low temps if needed for treatments for fishes.
You can take this system down between uses, but I find that it is always good to have u and running for those unexpected opportunities. I'm sure I left something out, but folks should be able to chime in on missing items.
hth