As many hamsters as you feel you can handle the responsibility for. Many hamster owners only have two, but if you want, you can have more. It's up to you ^-^
Most hamsters are nocturnal, so they are most active and playful at night.
Only one is born at a time
Yes the other answers right but if guineas or hamsters do they are normally not used to you (this goes for any animals) you should spend time with them.
Hamsters are fairly solitary animals and you may never be able to get to "strange" hamsters to become friends. I once had to dwarfs and they came from the petstore as baby brothers and they still didn't get along and we ended up having to separate them. You might just have to keep them separate. Note that hamsters do not need other hamsters company they would probably be happier without it. AS long as you spend plenty of time with them.
Hamsters don't get pregnant. They lay eggs. If your hamster has increased in size in a rapid period of time, you should probably see your local vet.
Dwarf hamsters reach sexual maturity around 4-5 weeks, which means they can get pregnant at that time. If you do not want a bunch of pregnant "baby" hamsters you should separate them before 4-5 weeks. At 3 weeks they are weaned and don't need their mom anymore. You can find happy new homes at that time.
3 but she needs to keep it a secret
hamsters like children as long as they don't wake them up in the day time and they should be kept away from other animals.
At 4 weeks, it is time to separate the pups from the mother and the females from the males. Keep the hamsters in their separate sex groups for another 2-3 weeks before selling them. At 6-7 weeks, the hamsters are now fully independent and are ready to go to their new homes.
About the same time that dwarf hamsters live
Hamsters can become less stimulating over time if you have exhausted all forms of interaction and stimulation for them. Introducing new toys, changing their environment, and spending quality time with them can help keep them engaged and prevent boredom. It's important to provide a stimulating environment to keep your hamster active and happy.
If you want to, technically its hibernation time for them, so all they would do is sleep.