Based on my experience:
1. Some, but not all trucks, need a hitch specific to their vehicle. (True or False)
Do not know but likely False
2. My 3500 needs a specific hitch rather than universal (True or False)
False
3. I don't need a slider (True or False)
True, especially for a long bed
4. Not sure what it means, but should get one that moves both horizontally and vertically
No, hitch should not move
5. Best brands?
B&W, Curt (I have a Curt), Blue Ox, Demco, Reese are some https://www.rvpartscountry.com/5th-w...hes_c_573.html
6. Do I need an install kit also (True or False)
False, if you have a factory puck system in your bed, otherwise you will
7. Can install it myself or should have professionals (myself or professionals)
you can install with a calibrated torque wrench, albeit I had mine installed since it required torquing to a specific spec and I wanted it done by local trailer shop
8. What should it be rated at for Maximum tow weight?
Get one that is over-rated from your fifth wheel, which is what I did since it does not add significant cost (I have a 24K albeit trailer is rated for 16.6K GVWR
9. What am I forgetting?
Suggest covering the hitch when not towing (I have a rollup black aluminum tonneau cover), check bolt torque for tightness and lube per manufacturer's inspection intervals, adjust height so bottom of trailer cab is level and 5.5 - 7" above the truck bed rail per manufacturer's instructions