You're request for full detail and then the subsequent questions don't quite match up. I don't mean any offense. I'm just saying that there's a lot more to exhaust, more specifically combustion and scavenging than say cats, resonators, etc. More of your questions are pertaining to sound, versus optimal exhaust design for power and/or particular engine characteristics (e.g. wanting to achieve a flatter torque curve). The thing you have to keep in mind is that the exhaust, like the intake, is part of the entire engine assembly.
Keep in mind that the engine mapping is done with the stock exhaust in mind. If you go with a less restrictive set-up (i.e. eliminate all cats and even possibly the muffler), you would have to revise the engine mapping accordingly to get the maxium power benefit. Note that contrary to popular belief, some level of resistance in the exhaust stream is not desirable. Aside from proper header designs that are tuned (look up helmholtz resonance) to help scavenge exhaust from each cylinder (due to pulse waves emitted from valves on reciprocating cylinders, which would be 180 deg out of phase), any additional exhaust component is unecessary from a power standpoint. Also note that to tune an exhaust header using the helmholtz theory, implies that the exhaust would be tuned specifically for a given rpm, so a compromise in design (i.e. header length) is usually made to allow for gains in power of greater range of rpm, at the expense of generating slightly less power.
As an aside, the S65's intake is designed much the same way. The large intake chamber, aside from being designed for optimal flow, also takes advantage of having an enclosed area where pulse waves from reciprocating cylinders can be matched.
Going back to exhaust systems, take a look at the current F1 cars. They're actually blowing the exhaust on their diffusors to create more downforce. In this case, the aerodynamic gains outweigh any small drop in power by routing the exhaust to the diffusor.
With respect to material choices, consider the facts (aside from availability/cost). It has to withstand high temperatures, must have a low coefficient of thermal expansion, must be easily formable (bends, butted areas, etc.), etc.
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