Set up a small business in the USA
May I consider a partnership to work in my business?
Is it necesary a minimun amount of money to set it up?
What visa do you recommend me?
First of all, being on OPT you have certain restrictions to what activities you can be involved in. So although technically anyone can own shares or member interest in US companies, you should be aware of all the restrictions your visa imposes on you. I would recommend you to consult an immigration attorney or a USCIS website to learn what those restrictions are.
As far as minimum amount to set up a business goes, there are no requirements to invest any money in a new business in Missouri, but of course you need to consider the potential expenses related to registration and day to day operations.