Nationality comes first, and it is not negotiable
The E-2 exists only for nationals of countries that hold a qualifying treaty with the United States. No amount of capital substitutes for it, and the list is maintained by the Department of State, not by USCIS.
Brazil is not on that list. This matters here because it is the single most common disappointment in this category among the people who write to us — a viable business, enough capital, and no treaty. Some people reach the E-2 through a second nationality; that is a question for the attorney, and it has to be real nationality, not residence.
Substantial has no number, and marginal has a definition
There is no minimum investment in the regulation. Substantial is proportional: it is weighed against the total cost of buying or creating the enterprise, so a lower-cost business requires a proportionally higher share of its cost to be invested. The money also has to be at risk and irrevocably committed — funds sitting in an account are not an investment.
Marginality is where otherwise good cases fail. 8 CFR 214.2(e)(15) calls an enterprise marginal when it does not have the present or future capacity to generate more than a minimal living for the investor and family. A new business can rely on reaching that capacity within five years, which means the projections are evidence and will be read as evidence.
The honest limitation
The E-2 renews indefinitely, which sounds like permanence and is not. It is non-immigrant status: it carries no path to a green card, the renewals depend on the business continuing to qualify, and the status ends if the business does.
People who want both usually need two plans running in parallel — the E-2 for presence and operation, and a separate permanent route on its own merits. Which permanent route, if any, fits a given record is exactly what the free assessment reads.