Mentrual cup question

Ok so im a tampon user and my sister told me about mentrual cups and ive read a lot about them... got a couple questions...

1. Do they hurt when they "pop open" up there?

2. How do you get it out? What if the suction is so good u cant get the thing out?

3. Can you sleep with one in?

4. How do you know what one to get? I have had 4 kids naturally probably a loose vagina hahahahaua but pap smearS hurt like hell. I use average normal tampons for my normal to heavy flow....