http://www.icalvyn.com/how-to-register-a-business/

Its a simple process. About Rm5 for business name, Rm60 for the license renewed yearly.

i put my house address as a business license.

Tax wise, you need to keep tabs on your profit loss. A bit of hassle, but if you're running at loss (operation cost > sales), your tax is exempted, and its also combined with your day to day salary tax.

You can be doing your own personal sales as side income, thats fine.
its particularly for those doing it full time. Without tax, or a steady income into a bank, it would be hard for you to get a loan if you want to purchase a house/car. Thats when a business current account comes in showing consistent income becomes helpful for you.