The more I get, the more I find I need.
I know I've seen this topic come up a few times (
http://weberkettleclub.com/forums/weber-kettles-accessories/how-many-kettles-do-you-need!/msg210723/#msg210723) and my answer evolves.
In my cooks over the last couple of weeks I've used my Gen2 performer, Genesis, WSM, 26" and Sam Adams 18", without really making it a point to using any of them-they just seemed like the right tool for those jobs. My 22" that I use for high heat stuff got subbed out at the last minute but its in pretty regular rotation too. I would say that the first 4 are the ones that I really would not want to do without, along with something to take to tailgates (currently have Weber Q and 2 SJGs for that) and that the extra 22/beater kettle and an 18" of some type come in handy. So that's 7 that I can come up with a legitimate reason to have.
The 26"er definitely held true to what everybody said, in that you don't know you need that much space until you have it and then, man is it a pleasant grilling experience. Last week I had ribs going on the WSM, and on the 26, put on two big foiled packets of potatoes, 3 sausages, 4 burgers and 6 hot dogs, and had plenty of room to move things around, utilize the indirect space, etc... I also find it comes in very handy when cooking a whole mess of something for the week, like a couple pounds of chicken thighs indirect. I'd always struggle with crowding/too close to the direct section trying to do that on a 22".
The performer is similar in that everybody said its awesome and will become your favorite grill. That's true (and when you have both, you'll realize why everybody says the 26" performer would be the perfect grill). I use the ignitor all the time on mine, even if cooking on something else, and that's generally where my current bag of charcoal, chimneys and grill brushes are stored. My performer is sort of my BBQ hub, where even if I'm not cooking on it, I'm using the table, lighting the coals, storing charcoal, etc...
The gasser is for when the GF is handling cooking (a priceless comment from her, when she was tasked with helping on the aforementioned 26" cook "Charcoal just doesn't get as hot" My response "That's because you have the lid off!"-she has no desire to consider using charcoal), quick stuff for after work or finishing something off when the coals are mostly kicked, a cook is almost done, and I just don't feel like adding anymore. Plus its an original generation red Genny so its pretty fun to use.
The WSM is for my smoking-its just so easy. It does its thing and I don't really have to fuss with it too much.
I have 2 SJGs and a Weber Q that cover my portability needs. Usually the Q, which also gets the call as a warming station or just extra space for burgers or dogs at a big party.
The 18's smaller footprint is great for the deck, and I usually fire it up if I'm just making lunch for one or two. It would get more use if it wasn't away from the rest of the herd.
Then I have a beater 22" red that I like and is already in rough shape (prior life, not my fault). I can use it for high heat and not feel guilty, while still cooking on a red.
An extra, black SSP is trying to quietly worm its way into the rotation, to take some of the abuse off of the 22" red and/or be a dedicated pizza/steak cooker.
So, I think that my "needs" are currently 8. My "haves" are more than that. (think the current count is 18). There's a bunch of other reds, a thumbscrew black and a limey. The explanation for those is just that they're cool! Most of them are in rehab, and once they're out and fully ready, I think they'll get cooked on when I feel like it (which is when my vintage red 18" gets used now). I'd like to have a 22" WSM for easier brisket and multiple racks of rib cooking, and I think it would be sweet to have a SCG, but I can't say I need either one (until I've added one and realized the this is awesome factor-see 26"er, performer above).
I can see that many people smoke on their kettles, especially the 26, obviating the need for the WSM. With 2 22s, you don't really need the 26", and you don't necessarily need a gas grill for convenience, or an 18 for efficiency. So could see an argument for the minimum being 3-1 SJ, 1 performer and 1 beater 22" (and preferably SJ, performer and 26" if possible). I think cutting back below that would strongly limit what I could do, without even considering convenience/coolness.
This is without really considering the vintage/collectibility aspect of it. There's plenty of those I'd like to have.