Nope. This is how it's actually done if you want to get the accurate cell count from which you can project how much of this slurry you'll need.
True, except that by the time the plates have grown enough that you can count colonies (1 over night and you can see them if you look closely, 2 over nights and you can count, but 3 overnights is easier) the viability of the culture may be different
If you're going to do the plating I would skip staining, that isn't as accurate.
But unless you are into all of that, I would just do what Sean says.
about 120 mL of slurry would be the target