Two Cresties maximum, i would advise just getting one female, when you know how to look after her, perhaps look to get a male in the future, but give the female at least 4-5 months to settle in on her own and for you to do the necessary reading up and talking to other keepers that you need to do. If you dont want to breed (incubating the eggs is very difficult and you risk your female getting eggbound and dying if you dont know what you are looking at and willing to pay one heck of a vetbill to save her!) you could get two females.
Bear in mind, they aren't the cheapest reptile on the market! Fairly slow growing = slow to breed = more money to raise = babies cost more
Low maintenance rep:
-viv
-forrest terrain substrate (holds the moisture)
-branches and vines and plastic (can use certain real!!) plants
-tub of Crestie Diet (and bowl for it) you might need to hand feed from your finger at first...well cute!
-tub of small crickets or locusts
-5% UV light