34-year-old complete beginner — just opened a Fidelity account with $100. Where do I start?

I’m 34 and just took my first step into investing by opening a Fidelity brokerage account and transferring in $100. Starting next month, I plan to contribute $200/month consistently.

I have zero investing experience and I’m looking for beginner-friendly guidance. Specifically:

1. What should I actually buy first with $100 in Fidelity? (Index funds? ETFs?)

2. Should I open a Roth IRA or stick with a regular brokerage account?

3. Is there a simple “set it and forget it” strategy for someone contributing $200/month?

4. What are common mistakes beginners make that I should avoid?

My goals are long-term wealth building, not looking for quick wins. I’ve heard about FXAIX and FZROX but not sure if those are right for me. Any advice appreciated!