No one can tell you how much to charge as there is much more info needed than simple measurements. Learning how to bid a paint job is primary to having a good business. Your experience painting will help you figure out how much labor and materials are needed to do a job.
To get the amount of paint or primer needed you will need to figure out the square footage of the walls and ceilings. This article will help explain this idea- <a href="https://www.house-painting-info.com/estimating-interior-paint-and-primer.html">Estimating The Amount Of Interior Paint And Primer Needed</a>
To get the best prices visit your local paint stores. They offer discounts to contractors for paints, primers and tools. Remember tools like brushes and rollers are typically used on more than one job so their cost will be paid upfront but recouped over time.
Other things you will need are any contractor licensing and insurance requirements for your state. Check with your state contractor licensing board for more details.