Hi. I have pool but confused about setup.

1. videos show pool being set up over grass, but we are also told surface has to be absolutely level and of course grass is bumpy and uneven. Do i have to dig up the lawn sod and lay sand down?
2. If yes, how deep to i go and how thick is the layer of sand?
3. How level is level. do i need to flatten it out with something from home depot, and get big level out there to make sure 's absolutely flat?
4. I see some people put down a layer of sand and then some kind of styrofoam. Some swear by this, others including Mermaid here in Ottawa say the stuff gets damaged and dented when kids are jumping on it, etc. Advice?
3. If i dig up and put down layer of sand do i need 2x6 or 2x8 hinged boards around it?