Ive played 3/6 at a few casinos in so cal, san manuel, pechanga, hustler, and soboba. All used only $1 chips. Id say 100 is good enough for the first buy but have at least another 100 in your pocket.

As far as the racks, some casinos dont let you use racks, like pechanga, others let you use the racks like soboba. I like having my chips out of a rack, but if im up to around 200 in chips, it can get a little messy and crowded, at san manuel I was sitting with about 250 and it got crowded, so I stacked 200 in the rack and left 50 to play, if I got down I just pulled another stack out. San manuels racks are particulary tight, and its funny to watch people try and pull a few chips out and then see 10 of them go flying. I agree dont play out of the rack but if the casino allows it, use it to keep your chips organized.