If you're going to do this right, start by putting an ammeter on your main house
battery bank and see how much you draw with your loads combined. Then figure in your latitude and estimated hours of full sun, and how many hours you expect to operate your loads. Also figure how many days of overcast you want to be able to handle with your
batteries. At best you'll be making a WAG about your needs.
If you're in the Northeast US you'll probably never get more than 85% of rated output from your
solar panels, your batteries and
solar charge controller might have a charge efficiency of perhaps 80%, and you'll get 4-6 hours of peak sun, perhaps 40% of the days will be overcast, you get the idea.
If you do the cost analysis you'll find it MUCH more cost effective to save
power by converting to
LED lights than by generating more power and adding battery capacity. You can also use the minimum backlight necessary to save power in your
Raymarine unit. You can find
cheap LEDs on eBay to replace the interior bulbs (search for LED and your bulb base type, e.g. MR11 or bayonet). For your nav lights it's more costly but a safer bet to buy from the nav light makers who claim to be CG Approved). The
anchor light is the most important to have as LED, as you're likely to run it more than any other nav light.
Another tip is to use an
MPPT controller and either wire two
panels in series or buy a
single panel rated for 24v systems. The
MPPT controller will do the stepdown to 12v but you'll get more power out of the system and charge for more hours per day. You'll also have less voltage drop in the wires between
panels and controller if you run at higher volts. (Don't forget
fuses.)
Once you put your system in place you'll also want to install a battery
monitor, so you have a better indication of how well your system is maintaining battery state. Battery monitors are like a
fuel gauge for your batteries.