Ask HN: What's your legal business structure and why?

Within the startup scene / indie hacker movement there is plenty of discussion about raising money (or not), marketing, building, hiring, etc. But I don't see much about the legal structure of the company.

I plan to keep my day job, but there are some things I'd like to build and invest in on the side: A couple SaaS ideas, maybe purchase some community sites, and maybe take funding someday.

LLC or C corp? Can I roll my Roth into it? Does a holding company make sense? What exit pain points could I avoid by structuring it a certain way?

What good resources are out there to learn?