Let's say I'm getting a G. Rosea for question purposes.. Though I like the idea of pink toes(A. Avicularia) too..
How often do T enclosures need cleaned?
Spot clean as needed, I do not spot clean mine every day. The biggest thing you have to worry about is making sure nothing is growing mold. Change substrate and do a good cleaning like 1 time a year.

Are uricating (sp?) hairs really a big deal?
If you are allergic then yes it is a BIG deal. If you are not then you will just be itchy. Be careful not to get them in your eyes. Be carefull not to breathe them in (Be very carefull if you have asthma). The worst hairs from what I understand are T blondi hairs. Remember that hairs fall off of the T and are present in the cage, so even if he/she does not kick hairs they are still in his/her cage. So if you go to pick up anything in the cage or stir up substrate there are hairs there too.

Best substrate?
I use coco fiber. But people also use peat, vermiculite or the mixture of the two. The down side to coco fiber is it comes in blocks that you have to add water to and then it takes forever for it to dry and is more expensive then peat. Downside to peat is it is kept outside and subect to any bugs and the weather elements outside (Though I know TONS of people who use it without any problems at all), upside not in block form and cheaper then coco. Vermiculite isn't used often alone but I know people who have good sucess using it by itself. Vermiculite is very light and does not seem very stable to me to use on it's own. But like I said I know people who use this with no problems. Comes down to what works best for you and your T's.

What about webbing? Do all T's make lots of web?
All T's can web. Not all T's web a lot. Out of the two you picked: The Rose hair will usually just lay down a mat of webbing on the floor (kinda like trip wire) and the pink toe will web a lot and will need height as oppose to floor space. Some people have psycho rosies (I do not). The pink toe is a sweet heart and more likely to shoot poo at you then bite. Pink toes are pretty fast compared to a rose hair.

Anyone been bitten? Want to share a story.
No I have never been bit. No stories to share here.