I have a pregnant cat and dont know how far along she is.?

Her belly is the size of a soft ball. When she is laying down i can feel the kitten/ kittens move, she has been laying on her side a lot and when i pet her she keeps rolling from side to side also when she walks she is stretching a lot. When does the milk start to come in and how soon after will she have the kittens? This is a first for me, I have been reading a lot and different web pages say different things. Also I have my cat down stairs in my laundry room area cause its quiet and away from ppl, if she goes into labor will i be able to hear her in case she has a hard time and needs to go to the vet? My room is upstairs and this is her first and last litter so i want to make sure she doesn't have any problems. Thanks