First off, congrats on the first brew. I'm suprised to see when people jump into all-grain right away, but you won't be dissappointed.
As for your questions...
1. This depends on what method you're using. Fly sparging should take at least a half hour, but this is just my personal opinion. Batch sparging (which you'll probably get better efficiency with when first starting out) should only take about 10 minutes. I usually add my sparge water to the mash tun, stir really well, let the grain bed settle for 5-10 minutes and then crank the ball-valve open and let 'er rip.
2. I don't like adding water after the fact. If your gravity comes out high pre-boil, then yes, you can add water to get it where it needs to be. Otherwise, I usually run all my extra water through the mash to make sure I get all the sugars rinsed out.
3. No. Do not add water after fermentation has already been started. You're just diluting the beer at this point. If you want to add water, it needs to be done before adding yeast. You also risk infecting the batch the more you mess with it after fermentation.
4. I suggest looking into a brewing calculator. I use BeerTools Pro, but there are plenty of others out there. These will calculate your efficiency as well as giving you the correct amount of water to add to your mash.