Designing great beers by Ray Daniels is a great book that covers beginner and intermediate brewing techniques. It also has the basics on designing beers of your own, and detailed information on different styles of beers. I would highly recommmend it.
I would not recommend adding more water to your wort at this point.
If you were to add water before you transferred your wort to your fermenter that would have been fine. However, the period after your wort cools and starts to ferment is very critical. Your goal is to allow your yeast to...
If something like this happens to you again I would recommend trying to boil down your wort to concentrate it.
My advice for you at this point would be to just roll with it and bottle your beer. It will probably lack some body, mouthfeel, and flavor, but it could make a decent summer beer...
It has been a little while since the post asking about how much priming sugar to add to a batch, but here goes anyway. This is a handy priming sugar addition calculator. It lets you account for what type of sugar you are using as well as the carbonation level you desire for your beer style...