Here a link about mobility in Ghent: https://stad.gent/en/mobility-ghent
Here the Dutch version with a bit more info: https://stad.gent/nl/mobiliteit-openbare-werken/mobiliteit-openbare-werken/park-and-ride-pr Under Betalend: Nee is free and Ja payed parking. Parking Gent-Sint-Pieters is expensive.
The P+R facilities are outside the circular road - R40 - around the historic center and so outside the Low-emission zone. In Google maps the R40 is highlighted yellow. Inside this road Ghent is notorious for it’s oneway streets and a challenge driving around. For directions best is contacting the place where you are going to stay. Also important to know is that foreign numberplates (except Dutch) need registration before entering the Low-emision zone as far as I know, but ask that too if that is still the case.
Living within an hour driving from Ghent I have no experience with overnight parking, so no idea about issues.