OP is in Coastal New England so shade and weather could complicate life for a 100 watt system.
But if you are doing this, install a controller and wiring capable of increasing your solar in the future without changing anything else.
If you have approximately 200 Amp/hrs of battery available and a single 100 watt you may well have all you need. Shading even 25% of your panel will drastically reduce its power output, so you may find that a second is needed if you dont get more than a couple hours of direct sun daily. Adding a panel is easy if you already have everything else set for it.
