Ultimately it depends on what you are going to use it for. I know, not the answer you want. But that's were you need to start planning. If you are going to use it for light loads like LED lights and cell phone or laptop, a small system is ok. If your going to use it for small appliances like coffee makers, toasters, hair drier for the significant other, entirely different system. Start with the size loads you intend on using and work backwards. How do you plan on charging batteries? How long will you be able to charge? Find the largest load you are going to use and get an inverter bigger than that. Note that motor type loads take a lot to get them started then taper off to keep them going. Don't skimp or you will regret it, trust me. The longer between charges the bigger the batteries. I prefer two six volt, but one big 12 volt will also work. I used two Interstate U2500 six volts that would do anything I could throw at them, then went to a 4D 12volt. The 12 volt was a disappointment after the dual sixes. Research the amp hr reserve of the batteries. A good calculator can be found at the inverter web sites, I chose Xantrex. Each system will differ, you just need to decide what you will use it for and your budget, that will dictate everything else.
