Hi Dan,
Quite a few questions wrapped into one post.
First, there is a significant difference between creating music (producing) and mixing music (DJ-ing). While the two are more and more found in the shape of DJ/Producers (or Producer/DJs 😀 ), it’s still relevant when it comes to picking things like software, hardware and such.
So, finding out if you will be primarily creating music and occassionally mixing or the other way around would be step one. The next step would be determining what workflow works for you. Then picking the matching software. Then determining budget and finally picking the right hardware to support all this.
If you plan on doing both equally (i.e. DJ and produce), you’ll probably find out that you’ll need more gear because you don’t want to compromise on either side.
For example, the Beatpad and the S4 are two totally different things. Picking between them is only useful if you know exactly what it is you are trying to achieve.
Let us know some more about your plans and we might be able to help you a little better.
Greetinx.