GTP's are arboreal snakes, so a humid hide would be as much use as a chocolate fireguard.
They average about 4' long, but some locales can reach 6' They require a fairly roomy viv as an adult with perches allowing the snake to choose it's preferred temp. They are very much a look but don't touch snake, as they are very fragile as youngsters and can be very snappy as adults.
Temp and humidity wise, a basking spot of about 82F with a temperature gradient from one side of the viv to the other and from top to bottom too, humididty shouldn't be constantly high. It's best to allow it to "cycle" throughout the day. Spray the viv in the morning and allow the viv to dry out through the day. They do need good ventilation.
Buy UK captive bred, preferably from a breeder, not a shop. Expect to pay about £375-400 for a neonate of a "normal" locale ( Sorong, Biak, Aru etc)
Avoid paying top dollar for so called "high yellow" babies as they change colour between six months and three years old and you may find that your High yellow baby turns all green.
Before lashing out with the money tho', get hold of a copy of Greg Maxwell's book "The more complete chondro" and talk to some of the breeders on here