I hand count out 12 coals to light. I have also recently found a huge difference between sprinkling those lit across the top vs pouring a little donut hole in the center. The donut hole gives me much more control and a slowing overall ignite. My theory is sprinkling across the top lights all the others exponentially as opposed to creating a burn line. I run with an empty pan and clay saucer and can run at 200 for making bacon.
I see no one pointed out that 250-275 is ok for good bbq, but I get having a desired target temp of your choice