akira - I was in your shoes about 4 years ago. I got interested after I wrote a couple of tracks in FL Studio. I bought a new computer, Reason 3.0 and a soundcard with MIDI (MAudio Delta 1010LT, which is still warmly regarded, even if it's not the best). With moderate effort I outgrew my setup within less than two years, then upgraded to Cubase 4, which is magnificent.
My recommendation to you would be to skip many expensive and time-consuming steps and get yourself a half-decent soundcard and Cubase, both of which you can find used if money is an issue. Also make sure you have the fastest computer you can afford, one that you can upgrade as the need arises. Speed makes all the difference. You can have great gear but a slow computer will more than likely kill your inspiration.
No matter what you decide on, making electronic music is always going to have a fairly steep learning curve (your effort will be the most important driving factor), so you're better off having the right equipment to start with and learn with. If I'd known better, that's what I would have done. In other words, don't be intimidated by this stuff - you, just like many, many people, can master it if you put in a modicum of effort.
FL Studio can be very powerful in the right hands, and offers more flexibility than Reason, which is also very powerful and extremely sturdy, but ultimately limited.
If you're interested, but not interested enough at the moment to splurge on a bunch of equipment, I'd say, one, forget Reason. Two, get yourself a half-decent soundcard with MIDI inputs so that you can hook up your Yamaha and use it as a controller with FL Studio. Three, if you like the process thus far, get Cubase as soon as possible, before you get all warm and fuzzy with FL Studio and don't want to part with it.
The main advantage to programs like FL Studio and Cubase - not Reason - is that when you're ready you can acquire, for free and/or for money, software synthesizers and effects (VSTis) that will greatly expand upon the palette with which you can paint your music.