To attach the carpet i use an air-powered staple gun. The staples are crown staples, the kind that carpentars use to attach crown moulding to the wall (the pretty wooden strips that line a room's ceiling).
And "Yes" i have shot myself once in the thumb with one of those suckers. OUCH!

The carpet i use is the kind that comes in the rolls that is used for carpeting household floors. I try to get the best quality stuff (like how some places guarentee their rugs for up to 20 years). This does wonders for durability.
How long the tree lasts pretty much depends on how "active" your kitty is (scratching repeatedly in the same spot, etc). It won't ruin the tree entirely, you just might need to trim a few stray strains of carpet once in a while. The first tree i made has lasted me 2 years with 5 cats, and it still looks to be brand new.
Tonight i was at the house of one lady that bought a tree for her NINE cats 6 months ago. They use the tree a ton, and it is doing very very well. It did have a lot of kitty hair sticking to it where they laid all the time, which the tree would look as new as the day that i brought it there if she gave it a good brushing.

Which leads to your last question. Yes, i do clean the hair off of my bonsai tree (and all my cat trees.) I use this brush that has a "velvety" surface that picks up all the hair when you brush it in the correct direction. I think it is originally supposed to used on normal furnature, but it works very well for the bonsai's.

My Aunt has also turned my attention to this other tool that it supposed to be for combing your cat. It's like a half wire loop with dull, saw-like teeth on one side and held together with a leather handle. She used it on her trees. I tried it the other day, and i must say that it works quite well.