2006 Ford Fiesta Leak? Strange smell

Im literally at my wits end. I bought this car off a private seller a couple of days ago and obviously didn't check well enough. The car felt extremely damp on the inside when it got cold at night, it felt fine during the day. And there was a lot of condensation on the inside of the windshield. I noticed two small chips on the windshield, but I also noticed there was dampness on the drivers side footwell, underneath the mat? The mat was bone dry on top? I've been trawling forums and online all day and people are bringing up the heater matrix and some kind of coolant leak? Im praying to god this isn't the case and that the windshield is the most likely cause of the damp. But I'm not sure. Has anyone got any ideas at all?