Hi, lots of questions there let me answer just the ones I know for sure on our old boat.
Old sets, ours IC-M700, work just fine for sailmail, weatherfax, and has for years with just a low powered dell laptop with usb to serial converter. we did get a Pactor 11e 10 years ago, and got the upgrade to 111. All works well.
Just a note, however, as a backup, which is now the primary, an Iridium phone, with good client, for about 80 cents, gets us weatherfax, Nandi fleet report, etc and sends and receives a few emails (not dead yet report to granny, etc, while underway) and no waiting to get hooked up, dial, and 47 to 57 seconds later, all done....and nearly no amp draw, so the backup has become the primary, and we use HF way less than in the past.
One other thing that rocks, is the Frampton GPS driver that allows use of Goggle earth and puts your position on it very accurately. 5,000 feet to 10,000 feet gives you crystal clear air view of coral, sandy spots to anchor, reefs, way better than charts, chartplotters anything else we have used in 40 years, including sitting on the spreaders conning. Bonus, if the view is not perfect in the current year, you can back up a year or two to when the view was good....caching Fiji took about 2 hours, so plan ahead when internet is good....