First thing I would do is stick to
one chart format. ENC's are good but even the US has not created ENC's for all their charts yet. (ENC's are in part created from raster charts. If your trying to cost effectively manage chart costs and disgusted / confused with all the manufacturers proprietizing their ridiculously over-priced vector charts making it impossible to use your charts on a backup plotter and a brain-strain to transfer waypoints, routes and tracks, then I would stick to raster charts and use your
laptop as your primary navigator / plotter. Keep your C120W as a MFD or backup plotter for those areas you already have maps for. Better you had a stand alone GPS versus the C120W internal but to do this, connect the C120w
nmea out to your
laptop then use the laptop nmea output to connect to the C120W nmea in. (this may cause problems and you might have to turn some nmea sentences off in your C120W). In doing this even though you may not have charts for a particular area on the C120W, you will still see your waypoints, routes and tracks on its built in world map. There is likely a better way but I am not familiar with the C120W capabilities.
Remember all your charts on the C120W will eventually need updating and a continual drain on your wallet but with the laptop and NOAA charts it's full coverage and its free.
Answers to questions:
1/yes
2/yes, don't know about a mac.
3/If you can use other formats on Raymarine C series its news to me. Nmea can not be used to transfer charts.
4/A mac person can help here but on a windows machine the nmea wires to the
serial port, or USB if you have a
serial to USB adapter.
Your on the right track using your laptop as a plotter if your looking to control costs. No they are not ideally suited to a
marine environment but good used ones are dirt
cheap, can be bought in Botswanaland and can be replaced a dozen times for the cost of one headache filled proprietary
chartplotter with all their infernal tricks that force you to keep paying and paying and paying.
Note: As I
recall, Raymarine has expensive laptop
navigation software that will interface with your C120W and will allow your
navionics to be displayed on the lap top. Best confirm this though.