Size of solar depends upon your usage. For storage only and battery maintenance then 100W might be OK. Otherwise do an energy audit to determine what you need for solar. Info/calcuators available on line.
The better question: "Is the solar large enough for my needs?"
Being critical: Salesman "Comes compete with solar" ie Total nonsense until you know it's capability and YOUR needs.
Measure the battery voltage, turn the solar controller on and the voltage should start for rise. Assumes battery a little discharged. Even better if you have a battery monitor that measures voltage, amps and battery charge state.