I had a 20' 14K (16' tilt and 4' stationary) gravity tilt-bed for the past 2 years.
The concern for loading non-mobile stuff on the trailer and then tilting to unload is a very valid problem. This means that everything (brush, dirt, etc.) must be loaded towards the rear of the trailer in order for the bed to tilt and help with unloading. Forget the stationary deck!
It's a PITA...
I never really had an issue with loading multiple attachments or additional implements (besides my tractor), however. It was simply a matter of unloading the tractor first and then using the FEL to pick the other implement off the trailer.
The hyd cylinder on the deck (double-acting) was already plumbed for power up/power down - it was just plugged at the top and bottom of the cylinder. All I needed was the fitting's and hoses and the 12v electric pump.
That said -- there is/was one thing that I appreciated more than anything else in the gravity tilt over the power up/down option: when the deck was slippery (especially in fall-early winter) and it's dangerous getting the machine up the tilted deck; I never had to have a 2nd person on the spot to begin dropping the deck IMMEDIATELY, before the tractor began to slide backwards off the trailer!
As soon as the pivot point on the tilt was achieved - the bed would begin to drop. I couldn't imagine trying to hold the tractor on the slippery deck and then trying to get off and power the deck down...
One caveat on using a gravity tilt-bed trailer - IMO - put your truck in neutral and use wheel chocks when loading and unloading. Especially with heavy loads. I loaded a JD 50D excavator on my trailer this past Nov. and the "push" against the truck when the bed dropped was SCARY!!
AKfish