firstly you're going to need a soundcard. Some pretty reasonable and cheap USB ones around for starting out. Just do some research to make sure you wont have any comparability problems with your existing hardware.
MPC are good for building beats and sample based music, but if you want to have easy control over individual notes and use alot of synths they will be limiting. I'd say your best bet is to focus on using your PC since you've already got that and your controller - the outlay cost will be cheaper, all you will need it a reasonable soundcard.
Can't recommend Reason enough for starting out with. It is a limiting software, but that will work in your favor as the learning curve will be a bit less steep for you. You will know when you have outgrown it, and then it will be a case of rewiring it to your new chosen DAW and making the transition.
It is not the best for using large chunks of audio, however. So, if you plan on sampling whole bars of existing music (likley with hiphop possibly?) it may not work that well for you. You have to feed all your audio through one of the samplers, which are generally geared towards being played as either individual drum hits or as building blocks to a pad/lead etc. Good or processing/bending/layering/playing the audio but not good for editing it/chopping it up or syncing and existing rhythm it your sequencers tempo. You can overcome this a bit if you use an external editing program like soundforge, or propellerheads recycle which will chop loops up into REX files that you can import into reason and easily sync and chop up, so it's not the end of the world if you want to do a little bit of that kind of thing.
Reason will force you to learn the basics of sound synthesis without getting too lost in mountains of VST's or a complicated 'profession style' interface.
Beyond that, only experience I've had is with cubase and ableton. Cubase will dramatically increased the sonic quality of your tunes over Reason. you will get much better mixdowns out of it, with VST's etc, but for actual composition in the end slowed me down a bit because I found it less hands on for midi etc. Always makes me feel like my hands were tied behind me back when writing, I feel like I'm
dictating to it, rather than
playing it. In short, I can get better sounding tunes out of it, they are just either not as good or a little awkward and slow to compose in the first place. For working with audio stems I find it's fantastic, however, so I reach for it when I need to do a finial mixdown on something.
Ableton is fantastic, very versatile and capable. It's particularly good if you want to do live work, or if you just want the writing stage to feel more
live. You could probably do a bit better diving into that first up compared to cubase, but still might end up spread your learning a bit thin over the ground as there are so many different things you can do with it, and you can still pile in more VST plugins than you will know what to do with. I'd still recommend reason over albeton for starting out IMHO.
You will also need something to monitor your music through. To start with headphones might be a good idea? IMO you can get better quality sound for the dollar compared to speakers, and it will remove the difficulties of dealing with how your listening environment chews up the sound. The problem with headphones is that they are not very physical, so sometimes you wont get as excited about the music as the bass wont be hitting you in the chest. You can always get that effect from a home stereo with a bit of bottom end though. If you find yourself getting serious and wanting accurate loudspeakers then fork out for monitors later on imo.
I managed to get 2 12"s out of reason, a basic midi keyboard and a pair of senheisser HD212 Pros, so it's definitely possible to have some success on a budget setup.
plus, there is the danger of just playing with your gear as apposed to making music, which I sometimes am guilty off since accumulating more shiny toys with flashing lights
of course that's just my take, you will probably get other people who will advise you to get a top of the range Macbook, Logic and a pair of genelec monitors from the get-go to avoid wasting time, but yanno. heh.
