I know what pushing the limit is about. I pulled my boat (an '87 Ski Centurion, like a Ski Nautique) about 3,000 lbs with a mid size '85 Ford LTD wagon. This is not a big car and I discovered early in the journey (from VT to PA) that the trailer brakes weren’t working. The feeling of a trailer in effect pushing my car when I tryed to brake was about as scarey as it gets. In my case I’m just the voice of experience trying to highlight some of the issues your enthusiasm may tend to mitigate. What we do for our boats!
One other thing to consider: gauges. I don’t know what your Freestar has, but often a factory ‘gauge’ is more of a low/medium/high display. I’d want accurate water temp, oil temp, oil pressure, and (maybe) trans. temp gauges.