Which machine and software depends on the niche you plan on targeting. Machines are available in single head, single needle configurations on up to over 30 heads with multiple needles per head. If you plan on doing jacket backs you need to make sure your machine has a large enough sewing field. If you want to do caps make sure the machine has finished cap capabilities. Do you plan on doing sweatshirt fronts, look at a machine that has tubular sewing capabilities.
Software also comes in a wide range of configurations.
You might only need a lettering package. Maybe you want to create designs for your own use or supply designs to other embroiderers. Look for a system that can grow with you. See the FAQ on digitizing too. You might need other equipment depending on your market.