ONe thing to add. Take the advice of listening to the modules first. An XP30 might be the right one butg then again, it might not. You should isten to the many, many great offerings available. For instance, a Motif module, Triton module, Proteus module or, maybe one of the other Roland modules.
Also, if you only want "real" instruments, then a sampler dedicated to this taks will give better results than a more "all-in-one" synth. As Mikeh said, the good libraries can ge expensive and, the samplers and computing power needed can become a factor. when you get into the soft sampler area, it matters whether you are on PC or Mac and how fast you computer is.
As for soft samplers, currently, there are two direct from disc offerings that I know of, Gigastudio and Kontakt. Gigs is PC only, Kontakt, Mac and PC I believe. This is good because it reduces the amount of Ram needed by the sampler thus not taxing the Ram used to record all that much and thus possibly avoiding the need for a seperate computer just for soft synths and soft samplers though that is a great option.
If mony is not a big deal, get a great contoller, another computer with another sound card (RME Hammerfall is popular for this). Load the second computer up with soft synths, soft samples and libraries of sounds and you will be on the cutting edge of sound technology.
With this configuration, you can use plug ins in the first computer for recording, effects, processing, shaping etc. and the second computer for the actual instruments.