All-grain introduces processes that take a few batches before you're consistent. There are a few brewing software which will do a lot of the math for you, so that things are somewhat predictable. I made a spreadsheet to do these calculations for me. Some good calculators can be found here: http://www.brewersfriend.com/ and a lot of equations for predicting volumes, gravity etc etc here: http://www.grimmysbeer.com/ If you scroll 2/3 - 3/4 of the way down, you'll find a lot of the stuff you're looking for, in terms of predicting how much wort you'll run off, etc.
To answer your questions:
1. If you're batch sparging it doesn't really matter how long you sparge, as long as you give it enough time for the remaining sugars to diffuse into the water. I typically see a lot of activity in the mash tun when I dump in the sparge water (lots of bubbles, swirling) and I usually just wait until that stops. 10-20 min is plenty of time to wait before draining. You can drain as fast as your system allows.
2. I wouldn't add water. Personally, I'd rather have less beer that tastes like it should than the right amount of beer but watered down. If, however, you're shooting for a low-gravity beer and you end up way high, I guess it could be done. Plus, 1.050 isn't outrageously high.
3. I'd be even less inclined to add water after fermentation. It'll just water down your beer.
4. Efficiency is one of those things that is often misunderstood. I'd recommend reading Kaiser's writeup here: http://braukaiser.com/wiki/index.php...ing_Efficiency but the above website with the equations has some simple calculations for efficiency as well. Understanding the difference between conversion and lauter efficiency is a big step towards identifying problems in your process and improving your beer.
Overall, it looks like you did well for a very first brew AND first all-grain. Have fun!