GN Soids Control has designed and manufactured many sets of hydrovac slurry treating systems to North America.
Here are some other questions that asked by our customers. In our system, we fixed 2.5inch opening gratings to catch rocks. Do you want to add a second grating with smaller openning？ 
Shaker Tank System GNXT7015-02 
What is back up plan if we experience surge runoff and/or rapid frequent plugging of coarse shaker ZKR-1230 wedge wire screen panels?
One of your workers should monitor the coarse shaker when hydrovac truck dumps into the catch hopper. So if he noticed surge run off of rapid plugging, will need to decrease the feeding, use high pressure water to flush the screen panel to clean thoroughly. In fact, all the screen panels must be cleaned thoroughly every other time in case they are blocked, especially the finer shaker and desilter shaker's screen panels. 
We know of other operations mostly converting to polyurethane of coarser 3 or 4 mm opening. Do you have these? Would coarsening plug pump?
2mm is advised by our customer, we do manufacture coarser opening screens. 
If changed to coarser opening, the submersible pump wears fast (such as the impeller), bearing also has a higher chance to broke when the duty increased. There is not specific data we can give due the slurry varies a lot. The good point is coarse shaker treating flow rate will be increased, while the discharged solids will be a little bit more moisture.   
In addition to coarser polyurethane screen openings, spray nozzles are mounted above screen often needing supplemental hosing beyond that.
BTW, GN Solids Control just provided another 4 sets hydrovac slurry treating systems to USA customers. In order to have a larger treating flow rate, we provided a decanter centrifuge from 22inch to a 30inch centrifuge.