2.  Absolutely not.  The TO 92 package is just a package.
The sizes shown here are not relative to each other. 

3.   With the flat face towards you, left to right, Enjoy British Columbia 

Whenever I think of this silly cue, I think of the Lumberjack song by Monty Python. 
Weather Reporter : "I yamma lumberjack, and I'm okay. I sleep all night. I work all day."
 Mounties : "He's a lumberjack, and he's okay. He ... "  dc

5.  a.  Dirction of the current flow, pointing towards ground.
     b.  It is always drawn on the emitter side.

6. Read the number.  If you really want to be impressed, check this web site.
    It cross references 40,000 types of transistors.
 www.ee.washington.edu/circuit_archive/parts/cross.html   and enter 2n3906.

7.  The pressure is in the system, whether the valve is on or off. 

8.  The capacitor is providing both voltage and current (power) to the transistor. 

9.  V+ to Diode, to Transistor (Collector => Emitter), to resistor, then LED. 

10.  You have got to do the work on this yourself. 
      a)  The answers will vary widely from one system to the next depending on the voltage available. 

      b)  The 100 mF cap will hold the LED on 8 to 10 times longer than the 10 mF cap. 

      c)  The 1000 mF cap will hold the LED on nearly 10 times longer than the 100 mF cap.