On your first question, I personally try to refrain from using strings of NOP's for delay purposes because each one only uses a single machine cycle. On an 8051 using a 12Mhz clock this gives a delay period of one microsecond. To achieve any significant delay or time period a string of NOP's would have to be looped. If an interrupt occurs during this loop then the entire ISR period becomes part of the timing process, making it very unreliable. The built in timers are much easier to use and provide more uniform time periods.
As for your second question I would think that the MOV instruction would be at the top of the list.
I'm afraid I can't help you on the third item. These microcontrollers were meant to interact with the outside world.

Hal