If you look at the front page of the electric training forum, there is a sticky, all you wanted to know about electric. Has tons of good stuff.
Simple answer to 1, is trainer, 75 to 100 watts per pound, 150 to 200 lots more fun
No real "simple" answer to 2 through 4.. I ran some number for 46 electric motor.
If I set it up with a 12x6 prop, 3s 4000mah battery I get 190 watts and 41 ounces of thrust.. Not a whole lot of power. Just changing to a 4s battery I get 390 watts with 70 ounces of thrust. Going to a 5s battery I get 675 watts and
101 ounces of thrust. ^s battery gives me 1048 watts and 137 ounces of thrust. Just changing the number of cells in the battery can have a huge impact on the power of the motor. Now if I wanted to use a 3 cell battery I would have to use a very large prop. If I use the first battery, a 3s 4000mah battery and a 19X6 prop, I get 542 watts with 99 ounces of thrust.
Yes it can get really confusing to learn all of this. Best advice is to double check your setup on here and to get a watt meter so you have less chance to let the magic smoke out of your electric setup.
Here is a calc tool you can use. http://www.ecalc.ch/motorcalc.htm?ecalc&lang=en