Kit Marsden's setup philosophy
Sounds grand, dunnit?!
Essentially, the idea is that each drum be equidistant from every other drum... The reasoning behind this idea is that it then takes the same amount of time to travel between any two drums in the kit, giving an even sound as you move around the kit... It should by now be obvious to the mathematically-minded that this is only possible with three drums or fewer... (I am not including the bass drum in this count, so we can assume that three drums means one snare drum, one rack tom and one floor tom...)
With three drums, however, it should be possible to set them up in a equilateral triangle... Clearly, this requires a 4pc (including bass drum) kit to work, so if you're trying to work out how to use this philosophy on your Nicko McBrain monster-kit, the answer is either to downsize, or learn Nicko's technique...
It is not uncommon to see people playing 4pc kits, and a lot of top players prefer them to 5pc kits... However, it often seems that people simply adapt a 5pc kit to make it a 4pc, rather than designing their 4pc "properly"...
Observe, the standard 5pc drumkit:

(Henceforth, in all diagrams, the bass drum shall be white, the snare drum shall be blue, any rack toms shall be red and the floor tom shall be green... There will be no cymbals included in these diagrams... All kits shown in the diagrams are set up for right-handed players - left-handed players should picture the kits reversed, or simply view their computer screen in a mirror!)
When people set up their 4pc kits, they look exactly the same as the one shown above, but with the second rack tom removed, thus:

We are therefore left with a gaping hole between the only remaining rack tom and the floor tom, making for uncomfortable movement around the kit... It would be far more ergonomically sound to move the single rack tom into the centre of the bass drum, as shown below:

Observe ye now the equilateral triangle, picked out in a gorgeous golden yellow:

Now some people may be reading this thinking something along the lines of but my ride cymbal goes in that gaping hole, how can I move my solitary rack tom over without disturbing the delicately balanced equilibrium of my drumkit?
The ride cymbal problem is easily overcome, however, by simply moving the ride cymbal to the right (left if you're left-handed) the same distance that you moved the rack tom...
Let's look at it this way - if you had removed the smaller of your two rack toms in order to turn your 5pc kit into a 4pc kit, your kit would look like this:

Would you then put your hihat into that gap?! I doubt it!
Then why put your ride cymbal into a similar gap on the other side of the kit?? By moving the ride cymbal into a more "hihat-like" position, you are actually making the kit more symetrical, and (theoretically) both easier to play and nicer to look at!
Hopefully, you're now rushing off to try these ideas on your own kit, but if you have stayed long enough to read this last bit, I'll leave you with this thought...
There are no rights or wrongs regarding drumkit setup - the ideas in my philosophy have been formulated over years of experimenting with different kit layouts... Trying out different things and discovering what works best for you is the only true way to find your ideal setup, so whilst I would urge you to consider my ideas, don't think of this as a "setup bible"...! In the end, you have to work out for yourself how you like your kit to be - it may end up looking like one of the diagrams on here, or it's quite possible it'll be totally different, all I can do is point you in what I feel to be the right direction, and hope you eventually end up where you want to go!
Appendage
Expanding the kit, now that the basics are in place, is certainly an option... Just as we put the ride cymbal, hihats and main crash in the best places, and then fill up other spaces with other crashes, splashes, chinas, accents, bells, electronic add-ons etc, we can leave the basic equilateral triangle set, and then put other drums in around them... Just as with bells, accent cymbals etc, these extra toms needn't be so easily accessible, as they're only used for specific purposes - most of the main playing is done on the central rack tom and floor tom, but at certain points in the music you may feel you'd like some more sounds available, and these can be tucked away almost anywhere, because you'll only travel to and from them in certain ways, certain directions, and at certain times...
I should probably also say that I don't buy into the whole "setup stereotyping" thing at all... The idea that you have to have a massive kit, with hundreds of "power" sized toms and two 26" bass drums to play rock or metal, or that you need a small 4pc kit with an 18" bass drum, two ride cymbals and no crashes to play jazz, or that you can't play funk music unless you have a 6pc kit in fusion sizes is absolute nonsense... The only factor which should dictate what setup you use is you - if you feel most comfortable on a standrd 5pc kit, then that's what you use, whether you're playing Count Basie numbers or prog rock cover tunes...
So, let's take a look at how this philosophy fits into some larger drumkit setups...
This first kit is a 6pc setup which has had two extra rack toms added - one either side of the "main" central rack tom:

And this next kit is also a 6pc, but this time with only two rack toms - however, a second floor tom has been added too, next to the "main" floor tom:

This third kit is a 7pc kit, which combines the ideas from the two different 6pc kits shown above - so here, we have three rack toms, and two floor toms, but the basic idea of the triangle is still in place, and it's clear that the extra drums are just auxiliaries:

And finally, a rather flamboyant 10pc setup, including four rack toms, three floor toms (one to the left of where the hihat would be) and an auxiliary snare over the two floor toms which are to the right:

