This caresheet should also apply to G.bisannulata, which is very similar in husbandry and difficulty.
Housing:
A 1-2 gallon container should work as an enclosure for a starter colony, once they start breeding you'll want to move them to a larger enclosure though, something at least five gallons should work as a permanent enclosure. They seem rather sensitive to overcrowding in my experience, and if crowded you'll likely see some nymph die offs. An airtight lid is probably unnecessary, just a tight one, only adults can climb and only males are very active above ground. The enclosure should have a moderate to high amount of ventilation.
They should be provided a substrate 2-4 inches deep, you can use plain coconut fiber, sphagnum peat, potting soil, or a rich mix of one or more of those and rotten wood, compost, etc., they really aren't that picky, though some say a well aerated substrate is best. About half the substrate should be kept moist, and the other half dry, horizontal or vertical humidity gradients can be used with success, but I personally think a vertical humidity gradient, (with the bottom inch or so moist, and the upper layers dry) works best for this species.
I'd personally recommend adding decaying leaf litter to the top of their substrate, as most Gyna seem to like feeding on it, though this species doesn't really seem to care for it all that much compared to fruits and proteins.
Substrate depth equals surface area for this species, (this whole genus really), above ground hides will seldom be used by anything other than adult males, and even they are fine with just digging into the substrate to rest.
Branches, bark pieces and other climbing materials can be added to the enclosure to give the males something to perch on and climb on to vent energy, but aren't really all that necessary.
Diet:
Dog/cat/chick feed, fruits and veggies seem to work just fine for this species, though they have a particular affinity for fruits. Pollen/artificial pollen can be offered as well, they seem to like it. This species has a much bigger appetite than other Gyna, so care should be taken not to accidentally starve them. Do NOT use food bowls with this species, for whatever reason the nymphs seem incapable of getting into food bowls and can starve or cannibalize heavily as a result.
While some older breeding reports claim that stone fruits like peaches are needed for optimal reproduction, this does not seem to be the case at all, most people who have thriving cultures of this species today haven't ever given their colonies stone fruits, mine personally seem to love chowing down on apples, even more so than banana, (which is normally the favorite food of Gyna adults in my experience).
Temperature:
Temps in the 80-88F° range are recommended for breeding.
They do not tolerate temperatures much below 50-40F° for long in my experience, (keep that in mind when shipping).
Breeding/Life cycle:
Adult males usually only live for 2-3 months, and likely lose their fertility in their last few weeks. Adult females live at least twice as long, and only seem to produce one or two litter of babies in their life, (probably from a single ootheca). While their internal oothecae contain 100+ eggs and fill up nearly their entire abdominal cavities, it can be hard to get females to give birth to litters of even a couple dozen nymphs. Big females may produce a lot more young than small females.
Nymphs take roughly 5-10 months to mature, with males usually maturing a month or two before females, if not sooner. For this reason, getting a young pair to mature at the same time can be a little difficult, which is why starting with a mixed group of nymphs at different growth rates is best.
This species does not tolerate crowding well in my experience, with high nymph die offs and halted growth when overly crowded. I'd say there shouldn't be more than two to three medium sized nymphs per square inch of substrate, otherwise you'll see problems. Females especially are prone to aborting ooths if bothered by nymphs, and so you may find it useful to isolate adult females to their own enclosure with a couple mature males when first starting out a colony. They're also quite sensitive to pest infestations.
Overall this is a bit of a challenging species to keep compared to other Gyna, and should be left to experienced breeders and those wanting a challenge.