How can we start a firm?

I just got 3 projects out of the blue from an old friend and I'm seriously considering striking out on my own. After all, there's never a perfect time, and if there was, this is probably it.

I'm very excited about the prospect of being my own boss, but I've never done it and am very young still (30f). I need help with the finance side, so I've come to our community for templates or examples of excel sheets anyone is willing to share.

Also, of course, anyone with experience striking out on their own? What did you learn?

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EDIT: Thank you to everyone replying. Your advice and words of encouragement mean so much to me. It's an intimidating task to take on, but knowing there's a community of us having gone through the same things makes me feel supported and so much more decided than I already was. THANK YOU! Let's keep paying it forward ♡ We're all in this together