Foreigner opening LLC and bank account on B1/B2 visa
Anyone can register an LLC in the US, and be listed as a company member. Restrictions would have to do with actual employment by this company, however ownership is typically is not restricted.
If you are physically present in the US you can open a bank account for this LLC, since you are physically present and can come to the bank. Remember to bring all the necessary documents, otherwise an account would not be opened (for a list of documents please visit our article "Banking in the US").