There are no restrictions.
Mr. Shusterman is a former INS Trial Attorney (1976-82) with over 35 years of immigration experience. His response to your question is general in nature, as not all the facts are known to him. You should retain an attorney experienced in immigration law to review all the facts in your case in order to receive advice specific to your case. Mr. Shusterman's statement above does not create an attorney/client relationship.
I agree with the other attorneys here. But also note that the business generally can't be one that's simply lending money to others. The business has to create or in some instances save jobs. With respect to a broker/dealer, be particularly careful about control person liabilities under state and federal securities laws, as well as the FINRA ownership process. In addition, you will be needing an attorney to assist in your due diligence on any deal in which you intend to invest, and especially so with the broker/dealer.
The foregoing is not legal advice nor is it in any manner whatsoever meant to create or impute an attorney/client relationship.