To find the idea you can simply copy a good idea that is already successful which you are interested in or come up with something unique

You can find people, but you need a really good idea that you can convince them to do for free or for a share; or you need money to pay tjem

You need a solid and in depth business plan with a team for any legit investments.

You will need someone to do the website for you or learn how to do it yourself, not an easy task. Use a friend that knows web design or hire someone local, you can negotiate a flat fee with them. After that you can start selling easily with a paypal account. If it takes off you’ll want to look into state sales tax, a DBA, and tax info. You can start a sole proprietorship no problem, but you should be using your own name as business name. Other than that, it costs about $90 to file a DBA.