I, too, am a Newbie to new digi modes and work EOC and community service. I first got Vara HF with Winlink to work by selecting FT-991 for Cat and NOT Yaesu's Standard COM port as mentioned in so many internet searches. I'm only using a USB cable to a WIN 10 laptop and it works just fine. I simply downloaded VarAC, installed it on the C: drive, followed instructions and got my first contact just yesterday.
I can see VarAC being very useful for EMCOMM in my area.