Great looking cook!
I am glad to hear you had a successful cook even though the road was a little bumpy. Being able to adapt to the situation is key for bbq!
As for controlling temps on the Weber. I haven't used a WSM before, so I wouldn't be able to tell you exactly what to do or how many lit coals to start with. I do know though, that once you get the temperatures stable, they are supposed to hold steady for long periods of time.
As for cooking at 225 degrees. Don't fight to hard with the cooker to get the temperatures down low. With time and experience you will know how to setup your cooker up and how many coals to start with to get the cooker to fall into a range of temperature 225-250ish, 250ish-275ish, 275-300ish, 300-325ish etc. I can setup a ring of fire on my kettles with a blind fold and have it run between 300-325 without blinking an eye. If you notice that with your bottom vents slightly open and it settles in at 250-275ish, cook at 250-275ish. It isn't worth the headache to try to drop the temperature down to 225 degrees.
P.S. is that afritada or menudo in the picture with the sliced brisket?