He means in the squad scheduling calendar, I forget where the menu is. It used to be that you pretty much had to reduce the number to 2-3 to get the little buggers to train properly. That no longer seems to be necessary, and you should leave it at the default unless you actually want fewer dwarves training for some reason.
I'm pretty sure wheelbarrows have worked that way since they were released. I've long used wheelbarrows to limit the number of jobs that can be spawned by a stockpile, so I can have a gigantic wood stockpile without crippling the fortress every time I cut a bunch of trees. The number of hauling jobs that can be spawned by a stockpile can be no larger than the number of wheelbarrows allocated to the stockpile or the number of empty spaces in the stockpile, whichever is smaller. If the items to be hauled aren't unreasonably heavy, you will get faster hauling with no wheelbarrows
I don't think the job priorities update changed wheelbarrow behavior (though bins were partly fixed), but it did reduce the number of haulers available by making dwarves prefer workshop jobs to hauling jobs. Since this lets you leave hauling enabled on important craftsdwarves, this actually dramatically increased the available haulers in my fort.
Tough luck on the gypsum plaster bug, though. That one's pretty annoying.