To get the most out of your inverter, you probably have to choose the inverter and match reasonable panel capacity to that. This is assuming that you want AC out of your project.

Depends. What do you want to accomplish? If you want to store the energy in batteries it depends on the size and type of your battery bank. If you want to run your entire house off of solar, look at your current electric bill to determine how much (KWH) you currently use.