Buying water gets expensive. Consider getting a "Whole House Filtration" unit from Lowes. You may also need some minerals to "soften" your water, but this would be a good start to cleaner and cheaper water. While I'm still trying to nail down my water parameters, this has been a nice addition to my setup, and makes it simple to filter the water right through your hose or faucet. Here is mine:
I got a shut-off and a couple Quick Disconnects so I can use my hose, and just hook it right up to either the filter or spray nozzle, or just use the shut-off fitting to have the hose handy for anything else, without having to run over and turn it off or on. Might be a little overkill for you, since I'm assuming your brewing extract in your kitchen, but the having some kind of filter in general helps save time and money.
I'd make the whole batch also, and not make any changes in ingredients(assuming this is a kit). I grew out of my 5g batches pretty quick. 2 cases of beer just isn't really a LOT, when you have friends/family over
It doesn't take much less time to do a smaller batch, so save your next brewday for ANOTHER 5g batch...to replace the one that you're about to brew and drink before you know it!!
As far as general advice, definitely get everything laid out BEFORE you start brewing, from hop additions, to your yeast, sanitizer, funnel, hydrometer, air-lock/stopper, water etc. BE CAREFUL if you have a glass carboy, they get heavy and slippery, especially when full. Handle with care.
Also your first few times you're going to be running around like a chicken with your head cut off, I don't think there is any getting around this, but being well-prepared will help you relax a little.
If you are using beersmith or some kind of brewing software, make sure you have your computer handy if you need to make any adjustments, or use any conversion/calculator tools. It also really helps to have your recipe printed off, or written down, along with a workflow of everything that you are going to do.
Lastly, TAKE THOROUGH NOTES!! It's hard when you're beginning to know what you NEED to write down, so just write EVERYTHING! It will really help to pinpoint parts of your process that you may have made a mistake or need to improve next time. If you don't have any reference to the details, you'll never know why "my first batch tasted a little off"...its hard enough to pin down off flavors when you DO write things down, but will be really good for future reference regardless. Write down how you managed your yeast, what the temp was when you pitched it, of course what KIND of yeast it was, etc. If you bought a kit, make sure you write down what ingredients were included in the kit, including all of the specialty grains, such as Crystal/Caramel Malt L#s(if its Crystal 20(C-20), Crystal 80, or whatever), what kind of extract was included and how much in each can.
MAKE SURE YOU MEASURE YOUR GRAVITY BEFORE YOU PITCH YOUR YEAST(as well as your temperature-make sure you've reached proper pitching temp), SO WHEN YOU GO TO MEASURE YOUR FINAL GRAVITY IN A FEW WEEKS(to assure of complete conversion and know when its time to bottle), YOU WILL KNOW EXACTLY HOW MUCH SUGARS WERE CONVERTED, AND MORE IMPORTANTLY, HOW MUCH ALCOHOL IS IN YOUR BREW
Most hydrometers are accurate at 60degrees, and come with a chart to adjust the OG depending on the temp. Usually if you're at 70degrees, you'll need to add 1 point to your gravity to be exact(1.052@70 degrees would actually be 1.053@60 degrees). Not a huge concern, but if you're at 80 degrees, you might think you didn't hit your gravity, when in all reality, you'd need to add 3 points because of the temp difference(based on your hydrometer).
On a side note, at some point it really helps to measure your equipment(carboy/kettles/etc). This way you know exactly what your beginning/end volume is. I bought a graduated cylinder, and measured out exactly 1/2g and 1g in a larger container(pitcher/pet food container), marked it at those points, and used that to measure out each gallon mark in my equipment(I haven't done my carboys yet, but my keggles and other pots are done). Then you can create a measuring stick to see how much volume is in your kettle. I got mine from a craft store. Was just a blank stick, kind of like a yard stick, that I marked up for each vessel and named them. You can also get a "sight-glass" from Bobby M, but you might want to wait until you've expanded your equipment a bit more for that.
Sorry for the endless rambling, but hopefully you got some good info out of it(and don't feel overwhelmed). It's really a pretty fool-proof process, and you'd be hard pressed to make something that isn't drinkable at minimum. Considering you don't have any homebrew yet...before you get started, grab a 6-er of your favorite microbrew from the store and ENJOY YOUR BREWDAY!
Welcome to the hobby/obsession!
