Im inluded the settings Im using in Pubg my FOV in PUBG is 103.

My monitor is 27inch 2560x1440 and Im using 800 DPI mouse.

Im trying to convert this to Fortnite.

But where do I set Vertical Sensitivity?

Is FOV always 80 in Fortnite?

Do I need to do 3 conversions one for hipfire, one for ADS and one for Scope?

The calculator will always try to match horizontal and vertical 1:1 since this is what most games use.

Since you have all the setting sin PUBG to the same value, this is MDH 100% in the conversion setup, so use that. FOV is locked in Fortnite yes.