While you can technically use your Montana Limited Liability Company (LLC) to operate a business, you probably shouldn't.
If you use visitor.us to help you buy a vehicle in the United States as an international visitor, we will form a Montana LLC, owned 100% by you. This LLC is a resident of Montana, and can therefore register a vehicle here.
There are two very good reasons why you should think twice before using your Montana LLC to operate a business.
First, if you are visiting the United States on a non-working visa (such as a B1-B2) or a visa waiver (e.g., an ESTA), you are not allowed to work (including managing a business that you own) while you are in the country. If you were to use your Montana LLC operate a business, you would need to ensure that a) you are outside of the country while managing the LLC's business, and/or b) you have appointed someone authorized to work in the United States to manage the business' affairs while you are in the country.
Second, while Montana offers sales tax efficiencies (vehicle registration in the state is taxed at 0%), it is not an income tax-efficient environment: business income is taxed at 6.75%, and personal income is taxed at 6.75% on taxable income over $19,800.
If you are serious about operating a business, you should consider operating it from within a legal entity formed in a state with 0% income tax rates. Your choices include Alaska, Florida, Nevada, South Dakota, South Dakota, Tennessee, Texas, Washington State, and Wyoming. The state of Delaware lightly taxes businesses, and offers a number of other business advantages.
In short, consult your immigration lawyer and tax advisor before using your Montana LLC to operate a business.