what are you running for electronics?

The garmin 162 looks like all I need for now with a high 300$ price tag. Heres the question It says I can down load software to it I assume if i'm going off Ri coast I can download a chart that will have info just lage a navchart and just superimpose my local on top of it correct? Other ? is I have a starboard t-top does this mean I'll need an external antena? I know my handheld garmin Etrex can't pick up in my car or house.