The quick answer is one unless you subdivide the tank. Sooner or later there is a chance that one animal will molt and another will kill it.
WIth lots of LR and cavities of different sizes, large tanks can support several stomatopods that live in cavities. It is not uncommon for a 90 gal to support three or four G. wennerae with only the occasional loss. This is not true of more aggressive, powerful species such as G. chiragra and it certainly is not true of burrowing smashers such as Odontodactylus.
Roy