One of the differences is the 12V are in parallel and 6V need be wired in series.
Need think of this in total battery bank capacity:
4x12V=8x6V, but the amps are different for 12volts.
The amp value of your 12V batteries, combined with the total number of bank batteries, will determine your inverter requirements.
Inverters are also, obviously, rated in watts and amps. The total household average hourly consumption needs to be considered. High-amp appliances such as panini toasters, irons and refrigerators are big amp-drawers. For something like this, a hight watt and amp rated inverter will be needed.
There is a great thread on this last month I believe by Cobraboy. It was very, very helpful. Use the search function.