1. are all the 5th wheel hitches the same basically? No some are better than others B&W, and Pullrite make very good hitches. Reese, all I can say is that there are a number of complaints about them from owners.
2. what should i look for in a used trailer and what should i avoid? There are a lot of lists online: search google for
RV Inspection List
When were were looking I was told to look in the basement and look up, if the ceiling of the basement is pressboard, not plywood, then the fver is cheaply built. Also someone advised me to look at the electrical box, if you can see behind it and the wires are neatly bundled then that is a good sign.
3. weight what should i stick to weight wise? my car trailer weighs 3500 pounds and I haul classic cars (heavy) pretty often.
The weight you need to mostly worry about is the pin weight of the fifth wheel when fully loaded vs the payload of the truck. The payload also includes passengers, luggage and misc stuff, the weight of the hitch ect. That is the limit most folks hit first. Figure the pin weight is roughly 20-25% of maximum weight.
Does your truck have the tow package (transmission coolers ect)?