Pregnant cat question

I found out last week that my one year old cat is pregnant. I found that her nipples had turned pink over the weekend so I took her to the my vet, they checked her and did an ultrasound and confirmed the pregnancy. My problem is that she never showed ANY signs of being in heat so I don't know how far along she is. She is starting to gain weight and i'm figuring she is around 5 weeks. When do they start showing?

They just said that she was 21 days or more. They also said that ultrasounds are hard to use for an accurate count of the kittens and want to do an x-ray in 2 weeks to see how many. She has medium length hair. She is a small, thin little girl. She used to feel weightless but now she feels heavier. Her belly isn't huge but when you see her from the top it rounds out on her sides. She used to like her belly rubbed but if you touch it now she growls. She is also very loving but cranky, too.

I have to admit that even though I didn't want kittens I can't wait for them to come. I am very excited and nervous. The vet I use I have been using for the last 7 years. I can call and ask questions at no cost. And yes it's $120.00 for the x-rays, that's $29.00 office visit, $55.00 1st x-ray, and $35.00 2nd x-ray if needed. We have an apt. for Friday April 2 for the x-rays. I know it's expensive but I really want to know how many to expect. My vet is also on call 24/7 so when it comes time for our kittens to come I can get help if it's needed. With 7 cats and 3 dogs they know us very well.
I am very worried about how she will be after the kittens come. I have read that sometimes the mothers will eat their babies in a misguided attempt to protect them. The only reason I fear this is that one of the other cats and the momma don't get along at all. I plan to lock the expecting mother in my daughters room and not let any of the other animals in there at all to give her a sense of privacy and a safe place for herself and the kittens but i'm not sure when i should start this. The momma normally does sleep in my daughters room anyway so I figured this to be the less stressful area. My daughter is almost 18 years old so it's not like she young and will disturb her too much. She really only goes in there to get dressed and sleep so Baby Girl would basically have the room to herself. Any opinions or advice would be greatly appreciated. Thank you.

As of right now Baby Girl growls and swats at all the other animals when they get within reach of her. This has only been going on since she became pregnant and i've read that it's normal behavior. I don't keep the others away right now except Freckles (the one she doesn't get along with at all) and T. Rexx (my pit bull mix) because he's goofy, clumsy, and tramples all the cats when he's excited. After birth I plan to slowly start letting the other animals (minus Freckles) start to get to know the kittens as Momma will allow. Never will I allow the Kittens to be in danger. This is why I will not let Freckles near them. She may hurt them because of the fued with the Momma.

I have already gotten her switched to a kitten food. I'm trying to make sure to keep her very healthy and hopefully the kittens too. She has always been very healthy so I'm hoping that helps. I really hope everything works out with the kittens but my first priority has to be to her. I can't wait for the kittens to come. They will be just as loved and spoiled as the rest. I'm not really worried about hand raising them if it's needed. A couple years ago my mother bred her White English Bulldog and the momma couldn't feed them due to an infection in her milk. We all took turns bottle feeding and everything else that was needed. All the puppies made it.