Best thing to do is to try it out.
Maximum sync speed is usually 1/250. That is the fastest shutter speed you can use and have the flash fill the whole scene.
Two stops down means two stops underexposed.
I think the two stops when balancing is just a bit of a guide. Your taste or style will affect this.
The point here is to underexpose to ambient light or just about the entire photo, then use the flash to bring your subject back up. This will make your subject pop a bit, and give it depth because the shadows will be emphasized. Just one of the many ways you can use your flash.
entry level is 1/200 as is my 5D.
also, I wouldn't always go with that as if your batteries in the triggers are a bit low you can get curtain shadows.
