Damian - Welcome to the Forum! You'll find a lot of helpful information in the past topics and posts. The folks on this forum represent thousands of cooks of experience on every kind of grilling and smoking.
Starting out as you are, the VERY best advice I can give you is (1) immediately order a copy of Gary Wiviott's book "Low and Slow" from Amazon.com (do it right now!), and (2) how ever you decide to do your butt for your company in June, do a full-scale practice run at least once before you do the cook for your friends.
Having graduated from a 22 inch Weber kettle to a WSM for smoking, I've got a little advice about smoking on the Weber Kettle. The biggest problem I had using the kettle for lower and slower cooking was keeping the temperatures DOWN to where I wanted them to be. I finally realized that to keep temps around 300 - 325, where I wanted them to be (I don't recommend trying to go really low and slow on the kettle - don't fret - you'll be getting yourself a WSM soon enough), I had to use only one bank of coals.
I also recommend putting in about a half chimney of unlit coals, banked to one side of the charcoal grate, put a disposable, half-sized aluminum pan next to the charcoal on the charcoal grate, set the bottom vents to about 20% open, then light about 10 briquettes and put those on top of the unlit (something of a Minion Method start for the charcoal).
It'll be really helpful if you have installed a thermometer on the lid of the Weber. I get mine at Academy.
Use your top vent to regulate the heat around 300-325 and plan on adding 5 - 6 charcoal briquettes every hour after the first hour or so.
How to add them? If you have one of the hinged grates, that's the easiest way. But you can get a cheap grate at Academy and use a dremmel tool to cut away some of the bars on one side so it's easier to drop in the coals. If you do that, just slide the lid to one side, keeping the meat covered to hold in heat, drop in your coals and put the lid back on - resist the desire to peek.
You'll need a good instant read meat thermometer. When the temp of the butt gets to about 160, wrap the meat in a thick layer of foil and let it keep on keeping on until the internal temp hits about 195. Pull the pork and let it rest, pull, sauce, eat, enjoy the accolades of your friends.
Using Weber Kettle as Smoker
Another link
There used to be a great diagram showing how to set up the Weber kettle as a smoker, but I can't find it on the net right now.
As far as the rub is concerned, I like the Chris Lilly rub and use it a lot. Don't worry about the quantity - make the full recipe and store whatever you don't need in an airtight bottle. I usually make a triple or quadruple recipe so I have more when I need it.
Good luck, let us know how it goes and post pictures!
Pat
