The more the better.
"the E-2 visa investment amount cannot be marginal and must be projected to make an economic impact. The return on your investment can’t simply provide for yourself and family, it must make a meaningful contribution to the American economy. The economic impact usually measures changes in business revenue, business profits, personal wages, and/or jobs."
From:
https://www.immi-usa.com/e2-visa-investment-amount/
The expectations need to be realistic, hiring just 2 full-time minimum wage employees can cost anywhere from $35000 to $85000 a year depending on state. Factor in other expenses such as rent, bills, stock...
If you said the investment was 250-500+ then I'd say you can be more confident of positive outcome.