Do I need a child theme?

I know if you are making significant changes to a theme, the safe way is to do all your customizations on the child theme. But I’m not clear at what point that is necessary — or if it is necessary for me in my case. Currently, I’m building my site based on a BoldGrid theme. I’m basically using the grids and tools BG makes available. I may remove or hide or add some elements, but nothing major. Am I okay to simply customize my parent theme in this way or do I need a child theme? I don’t want to get too far into things and realize I need a child. And if I do need a child: 1) How difficult is that to set up for someone who doesn’t know much about this, 2) If I already began building my site, do I just lose all those customizations when switching to the child? Thank you for your help!