The big question is have you thoroughly inspected the trailer, especially the roof and all seams that are potential water leaks? Do you know enough to inspect a trailer and/or have you considered having the trailer inspected by a RV repair shop? How old are the tires? Have the brakes been inspected? That should have been done before making a deal. Any trailer that is 5 years old or so may have issues, or if it was properly taken care of, could be ready to roll.
In any event, I hope things work out well for you and you can start having some great camping trips with your family. Enjoy!!