I kept my slings in small containers with a bit of peat to dig into/web around.
They like it dry as long as there's a water dish at all times -for a sling I guess you will want to keep the humidity a touch higher than for the adults.
I only gave them logs to climb on or web against as they got older - the Usambara used it as an anchor for some spectacular webbing.
Speaking of when they get their "attitude", I have had mine a very short time but they have THAT in spades.(And mine are still young) As to when they get it, somebody more qualified will have to answer.
IME, Right now i have 2 slings both marking the 1" mark, they have both moulted inmy care once, they are fast growers. You can also give them different setups, one of mine live in a delicup, with 2-3 inches of substrate (Eco Earth) and he/she burrows, my other one is also in a deli-cup with 1" of verm, and loves to web, so you can set them up in different ways, which is neat. The have an "attitude" known as "Orange Bitey things or Pterrors! lol" They are also very fast old world t's from Kenya in the Usambara mountains. My "semi-arboreal" sling has a leaf for a base of the web, while my burrower just burrows against the side. They get pretty big around 6" or more. They are little aggressive babys! You will love yours! They get orange/reddish when they are in subadult or adult colors! Hope his helped and Good Luck!
I kept my P. murinus on bone dry substrate, about 1" deep, when she was a sling. She built a web retreat, which I lightly misted about once a week. She showed signs of being defensive at about 2", but prefers to run into her retreat. She went from spiderling to adult(4.5") in about 2.5 years. I never payed any attention to, or worried about the humidity of her enclosure and she does fine.