Computer navigation software - I don't know where to begin...

[Steelcat]

OpenCpn is the best starting point.You can add radar, AIS, weatherfax etc if you want to.
Charts beyond free government areas are getting old (CM93)
You can make BSB/KAP Google Earth (Terraincognita) and Navionics charts (SAS planet) for specific areas.

Up to date charts are available for Android (Navionics) or Windows (i-Boating) at very reasonable cost.These programs are very basic (no AIS etc) but you do get legal charts.

For hardware I use Android Tv Box ($50) and Wintel Windows mini pc ($100), with VGA and DVI monitors.There are a lot of SSD mini PC's available now that use less than 10 watts and run on DC. Buy an extra for spare.