Would you consider these suggestions and allow time? I would recommend
taking the Virtual Reality tour of the Altar piece of the Mystic Lamb
at the Cathedral. It's a well done one-hour tour, and you need to book
timed tickets in advance.
I know this is an older thread and the OP might have already taken their trip, but I want to second the motion for the Altarpiece. I am not usually into art history all that much, but I have to say that this one blew me away. It was one of the most stunning pieces of ecclesiastical art I've ever seen. And the cathedral is breathtakingly beautiful inside (although the outside is a little plain as cathedrals go, so don't judge the book by its cover.)
Ghent was a spur of the moment trip for us (we "backpacked" overnight from France) and I absolutely loved it. And we saw a good bit in just a day and a half, although I hope to go back again.