For IRS purposes, you need to make a profit every 3 out of 5 years to have the IRS prove that you are not running a business. Otherwise, it is up to you to prove that you are running a business and not doing a hobby. You can prove that you are running a business by keeping your business accounts and personal accounts separate.

You can write off any legitimate business expense including dinners with clients, car expenses, equipment, etc.

Having a separate checking account and credit card is a good idea. However, it isn't necessary. You can comingle your business and personal expenses using your personal accounts. But, if you do this, then it will be harder for you to prove that you are running a business.

For your revenues, you don't need a corporate account to make you deposits. You just need to make the deposits in your separate account that you use for business.

You can read Publication 334 for more information.

Look around. Ask people around you.

How to start will depend on the idea – some businesses start part time until they get enough customers to move on – some start as web based businesses and others just have to bite the bullet and go bigtime. Whatever you do please do a business plan before you start – work out the details on profitability, time needed to make it work etc before you commit any money to the idea.
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