Software is the best thing to do next, but instead of argueing that, i'll argue something else
Microkorg: learn it in and out. Learn how to write your own patches properly. Delete all system patches and you'll be forced to learn quickly. It's not hard to do.
303? DON'T. There is no future in owning a machine that will cost you more than a computer and will probably only be used a couple times once you realize the lack of use for it in production. A microkorg can do everything the 303 can if you know how to use it. Of course, a sequencer would help with it, hardware ones do exist. It's much more flexible than something like a tb-303.
Electribes, in my experience, have been trash but really experiment with it and see what kind of workiable sounds you can get out of it. As for other drum machines, if you insist on going all hardware still, look for something else with some flexibility... there are lots of sampler/drum machine combos that will give you more flexibility and even better for your situation might be something like the Machinedrum (brought to you by the people who made SIDSTATION I think and capable of producing high quality sounds and even emulating your 808s and 909s if you really care to).
With a solid drum machine and synthesizer, you've got some good foundations going for beginning production and performance. In my opinion, the next very important step would be a sampler of some sort. I actually use a sampler when playing live and it's sort of what I "do" as half of tractile when playing live, although i am in essence doing what the other half ddoes with ableton, just with hardware and not nearly as flexibly.
For production though, I would definately reccomend tthat software comes into the mix somehow.. even if you set things up so you don't need it when you play live (funky edited vocal sampleing, etc - saved to a sampler), you will find that using just hardware is extremely limiting. Editing alone is extremely important in any sort of production and is often where all the fun and funk comes out. Writing on the computer (and combining tools like Reason and recordings from your microkorg) is a good way to go. If you try to record music done all with hardware without any thing else, I imagine it will come out sounding a little... well, I won't say any names or point fi fingers, but there's a few artists floating around over the past 3 years or so making some really boring music and all it needs is something a little extra that they would get from taking it into the software some more.
Hope some of this helps.
I'm not saying you should buy these 3, as you already have a microKorg and a nice Yamaha. But think before even saving up for a 303 
