You can find some generic advice online but you should ultimately get an immigration lawyer. Working with a larger company will make the visa situation easier as they have more resources- even Series A or later. It may be possible to sort it out as a founder, but that is likely more difficult (or at least expensive as I think the E-2 requires a significant investment). Some (eg, Skype, Zendesk) have founded the company in their home country and then moved to SF after they raised funding. If you have a special skill set (eg, PhD) there is also the O-1 visa.

Note: I am not a lawyer and this does not constitute legal advice.