1) As far as I know, the Fuel Pumps will gravity feed the engines if the pumps remain OFF. I do not turn the Center Tank Fuel Pumps ON (I leave them OFF) if they are empty.  Like you, it seems that they must be turned ON at some point, so I do that prior to engine start (which seems logical to me).

2) For takeoff, I think you are supposed to turn the Air Conditioning Pack Switches OFF and the Engine Start Switches to FLT. After the takeoff is successful, without an engine flame out, the Air Conditioning Pack Switches are turn back ON (needed for cabin pressurization) and the Engine Start Switches are turned OFF. Maybe the Engine Start Switches are supposed to be put in the LOW IGN position?

As I said in my earlier reply, I know there is more involved when it comes to a complete checklist. What I put in it was an abbreviated Engine Start checklist. ;)