If you do decide to make it a full-time business, the sky’s the limit. The house flipper/contractor that I worked for billed clients $35 per hour for painting, and paid his best painters perhaps half of that, so there is room for some profit there. Consider the case of Matt Shoup, who started with $100 and went door-to-door, asking neighbors if they needed some painting done, then built a painting business that earns $2.5 million per year!
It is very difficult to determine how a particular color will look on your walls, and with your lighting. If you have a color in mind, it is a good idea to buy a sample.

Before you go to the store to buy the paint, be sure to measure the square footage of the room—you don’t want to buy too little or too much.
Following is a list of tools that are typically helpful. Most of these are sold at home improvement centers or online. If you don’t already own or want to buy some of the pricier tools, you can often rent them. Garden hose with high-pressure nozzle Stiff-bristle brush with extension pole Bucket and detergent or TSP substitute Drop cloths, plastic sheeting, and painter’s tape Hook-blade paint scraper and molding scraper Wire brush Respirator, dust masks, and safety goggles Putty knife and 5-in-1 tool Work gloves and latex gloves Stepladder and/or extension ladder Disk sander or random-orbit sander and sandpaper Caulking gun and caulking compound Paintbrushes (see below for information about selecting) Paint rollers and extension poles 5-gallon bucket with roller grid Paint sprayer* (see below) Select the Right Paintbrushes