If I were just starting now, knowing what I know, these are the things that matter the most.
Boil Kettles
Get the largest boil kettle that you can afford. The northern brewer kit does not even come with a boil kettle! The other one only has a 5 gallon boil kettle. I do 5 gallon batch sizes for the most part and my boil kettle is 13 gallon capacity. You'll find out quickly that a 5 gallon batch in a 5 gallon boil kettle just doesn't work. First, you're going to be starting with 6.5 gallons preboil volume at least (mine is usually about 7.25 preboil volume). That preboil volume obviously does not fit into a 5 gallon boil kettle!
I sometimes do 10 gallon batches, so I'm starting with 12.25 gallons preboil. This is a really tight fit for my 13 gallon boil pot. I used to boil them separately, but since I discovered FermCap-S, I am no longer worried about boil overs in my 13 gallon kettle, even with a preboil volume of 12.25 gallons. I love the stuff.
Fermenters
Fermenters are another issue. Just as we have boil overs with boil kettles, we sometimes get blow off in our fermenters. This is because the yeast can sometimes create a large krausen that fills the head space of the fermenter and goes up through the airlock. I've even had it clog an airlock, build up enough pressure, and sent the airlock flying with foam up on my ceiling. So, as with boil kettles, it's nice to have some extra room.
I have the following fermenters:
3 gallon better bottle fermenter
These are plastic carboys made especially for fermentation. (by the way, water bottles that are sold with drinking water in them are not food safe, so they
are not acceptable for fermentation) I use these for split batches. Let's say that I brew 5 gallons of something and want to try two different yeast or put
fruit in one of them. I'll split the 5 gallons between these two fermenters for those types of experiments.
5.5 gallon plastic bucket fermenter
This was my very first fementer, and it came with a 5 gallon plastic bucket for secondary or bottling. Like you're considering, I started with a kit and these
are what came with my first kit. My boil kettle was an 8 gallon stainless steel kettle from a turkey fryer kit. I now use the 5.5 gallon fermenter and the 5
gallon bottling bucket for StarSan solution only. I use the 8 gallon boil pot for the occasional times when I make a 10 gallon batch of wort and then split the
wort into two 5 gallon batches that are hopped differently. One batch in the 13 gallon boil pot and one batch in the 8 gallon boil pot.
8 gallon plastic bucket fermenter
I have two of these. I use them mainly for primary fermentation of clean beers (I also make sours, but I won't put a souring beer in them, because once
you do that, you will probably never get the bacteria out of them again). They are ideal for primary, because they have about 2.5 gallons of headspace and
won't make it up to the airlock, so they will never need a blow off tube to avoid clogged airlocks.
5.5 gallon glass carboy fermenter
I have of two of these. I use them primarily for secondary fermentation or for extended aging or conditioning of sour beers. These were my first glass
carboy fermenters and these are the ones I learned about blow off being a problem.
6.5 gallon glass carboy fermenter
I have one of these. Not quite enough headspace for use as a primary, but I can use it in a pinch with advanced planning. For example, on lower gravity
beers that I use FermCap-S on, they usually won't blow off on this one. Without FermCap-S, they might blow off.
7.5 gallon glass carboy fermenter
I have three of these. I can use them for just about anything! Primary, secondary, extended aging. Doesn't matter with these.
To summarize fermenters:
I would get the largest that you can get in a plastic bucket for now. Just remember, if you only have one, then you have to wait to bottle, before you can
brew again.
Books:
Get John Palmers book "How to Brew" and read it cover to cover twice before you ever brew a batch. After that, pick and choose the books as they fit into your progression.
Other stuff you'll need to start brewing: If it is in italics, it's a must.
Fermenter See above for guidelines, since it's important to understand what you want when you get started.
Airlock with rubber stopper to fit your fermenters. If you have two fermenters, you need two airlocks, at least.
Fermometer (temperature strip to monitor temp. of beer) These stick onto the side of your fermenter. They aren't a must, but they are handy.
Hydrometer Jar (for easier reading of the hydrometer)
Hydrometer (to test sugar content of beer)
Muslin Grain Bag (for steeping specialty grains) This is a must for you, since you're starting with extract and you "will" want to steep grains.
Hop bags. I guess you could just throw your hops into your boil kettle and then let the funnel and strainer below strain them out as they go into
your fermenter. However, I love using hop bags, since I don't strain my wort.
Bottle Capper,
110 Bottle Caps (1/2 pound) This is enough for two 5 gallon batches.
Auto-Siphon, 4 ft Hose and Shut-Off Clamp
Bottle Filler
PBW (Powdered Brewers Wash) Cleaner
Bottle of Starsan sanitizer
Carboy Brush This is a must if you have chosen carboys for fementers.
8" Funnel Not necessary, but handy.
Handled Strainer (fits inside the funnel) Not necessary, but handy.
Beer Thief (for taking samples out of the carboy) Not necessary, but handy.
18" Long Brewing Spoon
Long Stem Thermometer with Clip
"How to Brew" by John Palmer I felt this was so important that I dedicated a section to it above!
Thin Wall Stainless Steel Pot (the largest you can afford) I also felt this was important enough to talk about above.
20 Foot Copper Wort Chiller To me this is a must, but I guess you could put the kettle down into an ice water bath to get down to yeast pitching
temperature. I consider it a must, because the faster you go from boiling to pitching yeast, the less likely you are to have a bacterial infection.
12 ounce Beer Bottles The amount you'll need is 54 bottles per 5 gallons of beer.
SUMMARY!!
Plan ahead for when you do go to all grain! If you settle for a 5 gallon pot, you'll be boiling less wort and then topping up in your fermenter. Once you go to all grain, you'll be doing full boils and that 5 gallon pot will be useless. I actually have a brewing friend who took his original 5 gallon brewing kettle and drilled holes in the bottom of it for drainage and he uses his as a pot for his hops that he grows.
You want to have as many purchases that you make up front be in equipment that you'll continue to use for years and years. My suggestion would be to look at what I've outlined here and find a kit that best fits the outline. If a kit is close, but is missing one or two things, just purchase those separately.
Don't skimp now, if you can help it, because if you skimp now, you'll end up paying for it again later (especially the boil pot!).
I hope that I've given you a little bit of help.