As Jamman says get a laptop, controller keyboard and some software.

I recommend Windows as they are usually cheaper and there are a boatload of free stuff out there (Mac users only have a limited amount) which will allow you to play around to your heart’s content.

Another route is to forgo Windows or Mac and use the free Linux OS, as again there are boatloads of free software for it, and you are not tied to the way Apple or Microsoft do things.

Native instrument Komplete soft synth package is probably one of the best all in one set, however you will have to pay for it (But you won’t regret it).

As to playing, if you’re doodling on the keyboard you are playing it.

As to the benefits of owning arranger keyboards, well they are easy play, (Press a button and everything is done for you) so that even if you have no talent you can sound great, and in the right hands they can sound good live, (Just remember to turn the automatics off and actually play it) but they are produced primarily for the home hobby player, (They basically took over from the home organ) hence there editing and setup capabilities are severely limiting compared to a workstation. (Interestingly a lot of home arranger players are now adding workstations to their arrangers, (Korgs Kronos and Krome really have taken the market by storm) and if it really takes off I can see some great arranger/workstation hybrids being introduced in the future)

Hope this helps

Bill