Electronic charts & SSB weather
"I want to get a weather fax, printer, hook up for the laptop, tied into the SSB. Like you say, tha computer has many uses."
I''d suggest you visit a few boats that have been out for a while and look at their set-ups, before making up a lengthy list of boxes. You''ll get a lot of ideas. And especially if you are motivated to have email aboard (and therefore be using a TNC), you will have many options for wx fax (text & graphics) without any need for a wx fax receiver or printer.
"I will be on 12 volt only while at sea, can lap tops be powered via 12 volts?"
See the discussion on this topic elsewhere. Again, lots of choices...