With fluff its a bit of what is written and a good lot of speculation/guesswork with what information you have. (I am severly regretting selling my Beasts of Chaos book right now as Beastmen were always a favorite army of mine.)
What is written is that they are not natural but are from both animals AND men mutated by warpstone dust and have since formed into a truely chaotic race. To partially quote on their intelligence: "...for although they have a semblance of the intelligence of a man, they employ it with the base cunning of a wild animal." I mention this as it surely has some reflection on what they can and cannot do in their unique 'culture'.
As rightly mentioned by Kuffy they form together in warbands and do not generally stay in one place for long. That said however there is reference to them raising and protecting herdstones in their ongoing struggle with the wood Elves for control of the great forests... so you can also probly assume they might stay in one place for an extended period if the stone was judged to be of some importance. Its probly more of a territory type of thing with them though as they abandon things as easilly as they create them... as it is with chaos.
For reference to their trials of leadership I do recommend you get your hands on the Beast of Chaos book as there is a great short story in there about a beastman earning the right to lead his herd... I'm pretty sure its Khazrak but as I said I sold my book so I'm not 100% on that. (regretting that desicion a bit more now... *twitch*)
Forging their own weapons is pretty much a matter of opinion: the models have items that certainly look like they could be metal and indeed many pictures show Beastmen with swords, chains and the like upon them. Whether these are simply looted, reminants of their former human exsistance, traded with the maurauder tribes or crudely made by the Beasts are all quite viable options. Due to the ritualistic importance placed on metalworking by tribes in our own past and the in game link with the maurauders based on those very tribes I like to assume that some Beastmen do have the ability to forge weapons, even if they are only using the more basic metals like copper, brass and iron. That said it is as viable that a great many Beastmen simply have stone and bone weapons. (Again echoing Kuffy
I think due to the fact GW aims its games at the age of 12+ that whole subject is glassed over and generally forgotten. However I believe there is some older fluff that says something about Beastmen being born directly from maurauder women on occasion. Also there is reference to the character Morghur having a mother so the possiblity of female beastmen is certainly not above the realms of possibility. (All the female humans and animals in the chaos wastes are surely not immune to warpstone are they?
I hope this helps... the Beastmen certainly are a facinating if rather brutal lot.