My advice is to get a lawyer right from the start. Many firms around here have programs for startups/entrepreneurs that delay any fees until you get a seed/A round > $50k.
They will also have "rules of thumb" for market based splitting formula.
They will have many boiler plate contracts.
I can recommend you to someone at King and Spalding, Pillsbury with such programs.
I can also recommend a really great small firm that is female led. Jessica Su.
You can tell her that I recommened you there. She will give you good advice.
Here is her site and pitch.http://www.sulegal.com/why/testimonials_2.php
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