I forgot about your hardware... I'd say:
My current gear set-up is as follows:
ZOOM MRT-3 RYTHEMTRAK (Good inexpensive drum machine)
ALESIS AIRSYNTH (not bad)
YAMAHA DJXIIB (my opinion...a lame a$$ toy)
RADIO SHACK SOUND FX Generator (vintage sh!t, real cheese, simple sound fx like glass brekaing, creaky doors, etc., can slow down/speedup/echo/reverse combine its sounds)
KORG ELECTRIBE Amk II (on order from Korg, looks real promising?)
You have some tools that you can continue to use, and some options for growth. You didn't mention a budget, so I'm going to assume from the pieces you have that you're working with a low to moderate budget, and you'd like to save a buck where you can (don't we all:) ) I'm also assuming that you're going to wind up going with an all-hardware rig, and you'll use the PC for recording (or go to a real studio).
From what you have, I see a few things:
1) You need more sound sources. Your synths are only one part apiece, so you're quite thin in synth voices.
2) You're going to find you're short on sequencing resources, probably sooner rather than later.
3) You don't have any sampling facilities, and that's really important if you're into cEvin Key
Having said that. I'll go down the list.
Zoom Rhythmtrack - I would ditch this box. Record each sound individually into your PC and save the wav file so you can use it later on when you get a sampler.
Alesis AirSynth - I see this as kind of an "icing on the cake" or "interesting toy" piece. It might serve as some visual "wow" at a live show, and you might get some decent effects type noises out of it, but it's not going to be your backbone tone generator.
Yamaha DJX-IIB - Ditch it.
Radio Shack Sound FX - Keep it. It's probably monetarily worthless, but I'm sure you can get some sample fodder out of it. Leave it at home when you play live though
Electribe A MKII - It's a usable piece, and it has a built in sequencer. 2 parts, meaning it can play two different sounds at the same time, but each voice is monotimbral, meaning it can only play one note at a time (per part). I probably wouldn't have bought it at your stage, since it's not something you can base your setup around - that's what you really need are some workhorse pieces. Since you've got it on the way we can work with it. This will definately be your best bit right now.
So, what would I do? Well, I'd try to address the above issues first, with the idea that you really need a real workhorse to build everything else around. I can suggest a few things:
For sequencing, I would pick up a secondhand Yamaha RM1X. Don't pay more than $225 or so on Ebay for one, and make sure the knobs aren't wobbly. While they do wobble eventually, they actually don't feel like they're going to break off, and my RM1X has had a lot of hours on it. The RM1X also includes a sample-based soundset that includes a variety of synth and drum sounds for techno. You'll want to get this piece first, because this can drive everything else in your rig and function as a sound source for a whil until you get the rest of your setup in place. Learn it top to bottom before adding any new gear, 'cause there is a lot to learn. Even though I have Sonar for sequencing, I still prefer to knock out patterns on the RM1X, then save them onto disk and load them into Sonar for arranging - this is a great compositional and live performance tool. It offers you lots of control over your sequences for playing live. Another option here might be the Emu Command Stations, which are similar machines. The RM1X is a better sequencer but the Emus are better sounding synths.
Secondly, you need to pick up either a workhorse synth, or a sampler. IMHO, the decision on which to go for first should come down to whether or not you want a real keyboard for playing parts by hand. If this doesn't interest you at all, I would rely on the synth you have in the Electribe and the one you'll get with the RM1X to hold you over for a while and go for a sampler first. Your cheapest bet for a good sampler is probably the Emu ESI-series (ESI-32, ESI-4000, and ESI-2000 in order of appearance). I'm an Akai user myself, but at a low price point I'd take an ESI over the Akai S2000 or S3000. Yamaha A-series (A3000, A4000, A5000) are a good option for a little more money. If sampling is going to be a large part of your sound I recommend you look into one of the Yamahas, and if you're going to commit a good chunk of cash, say $600-700, I would look at finding an Akai S5000 or Emu E-5000 sampler. All the samplers I've mentioned are pro samplers (as opposed to phrase samplers, like the Yamaha SU-700 & RS-7000, and Akai MPC-2000). Phrase samplers are pro pieces too, but a "pro" sampler will allow you to spread sounds across the keyboard, like a piano patch or a sampled orchestra. Phrase samples don't let you do this - they just play back whatever phrase they sampled. Pro samplers can obviously work that way too, so you get more flexibility this way.
If you do decide you want to play the keyboard, then I'd look at a synth first. If you have the money to spend, you can find a keyboard version of many good synths. However, the rack versions are generally much cheaper on the used market. Good candidates here will offer you a good amount of voices and parts. You're likely going to want a virtual analog synth, and there are lots to choose from. The Nord Lead is a great synth in a low price range. I'd look for a Nord Lead II if you decide to go this route, and expect to pay around $650 used for a keyboard and about $400 or so for the rack version. The Access Virus in it's original spec is a good choice. It also came in B and C flavors which are more powerful and much pricier, although if you can score a good deal on a B go for it. The A's go for about $450 used, and they didn't come in a keyboard version. A used B-spec KB will still run you around $900, so it's not that attractive of an option. The Waldorf MicroQ sounds real nice, and it's cheap too, but it's a bit hard to figure out how to edit it. I'd stay away from the roland JP series synths - they don't offer you enough voices. The Novation Nova and Supernova are also pretty cheap secondhand and will really serve you well.
In terms of saving money, it'd probably be cheaper to buy a controller keyboard - like the ones MIDIMan and Evolution make, or even a used Yamaha CS1X or something - than to buy a keyboard version of a good virtual analog synth. But it is nice to have the synth editing controls right on the playing surface too.
FYI, I use an RM1X, Akai S6000 sampler, Nord Lead I keyboard, Yamaha CS1X keyboard, Access Virus (original spec), and a Waldorf Attack drum synthesizer in my rig. I've collected this stuff over the last 6 years, so slow and steady is the way to go. Learn each piece throoughly before you move on to a new piece. You'll be able to get a lot of mileage out of an RM1X and your Electribe if you learn those two pieces really well. Adding a sampler onto that really gives you pretty much anything you'll need, unless you decide you really want to go all out and dedicate serious coin to your hardware (which is basically what I ended up doing).
Good luck. Let me know if you need any more assistance.