In My honest opining buy the biggest trailer you can afford. Toy haulers fill up fast and the size you thought you needed will end up being too small.
Also, being the truck you have, you could go 5th wheel as well. I have owned two tow behinds and now have a 5th wheel and the difference in towing is night and day.
I used a WD hitch on both trailers and felt it helped with rear sag plus the anti sway help a bunch as well.
Dumping is not bad at all. Make sure you use a really good chemical and there smell is very minimal.