It depends on the energy needs and the geographic location of the system. The number of panels needed is deduced by hours of daily radiation. If the system is installed on a mobile vehicle, like a boat, must make sure that the panels loads in the shortest time possible by calculating the equivalent hours, that is the number of hours in which the panel is operating at maximum power.
The power required and measured in Wh, depends on how and how much you plan to use appliances and various equipment. The installation for a house isolated from the electrical grid should be well-thought.
The Lithium-Ion technology is totally different from the one used in traditional lead-acid batteries. Lithium-Ion batteries are lighter and benefit from a higher capacity.
If the solar panel is applied on an unmovable structure, such as a roof, the optimal angle at our latitude varies between 25 and 35 degrees with south (Azimuth) orientation.
Solar panel does not require any special maintenance, just keep it clean. Clean with water using a non-abrasive damp cloth.