Congrats on your first all-grain brewing effort! I'm sure your beer will turn out wonderful and probably a really nice session beer.
Awesome advice in this thread. Water, being the ingredient that makes up the highest percentage of beer, needs the most attention. Listening to lots of pod casts I heard over and over that it was the last thing that should be tweaked once your process is dialed in. JMHO, it's worth starting early because it's a subject that takes more time to grasp. The other juicy tidbits are a bit easier to implement. Ward Labs offers water tests for under $17 that will give you all the details required. John Palmer's spreadsheet is excellent. Once implemented, this tool helped increase my efficiency from the mid 60's to the 78-82% range.
On the subject of accurate volumes, one of the best tools is a long spoon or mash paddle with markings for every .5 gallons calibrated for your kettle and then calibrated for your carboy on the opposite side. This will give you some confidence when you calculate your efficiency into the kettle, the fermentor and overall brewhouse efficiency. You can mark the outside of your carboy with a magic marker for every half gallon. However, I find the markings wear off rapidly, especially if ferment your beer in water baths.