There are probably other people who know more about all the different options than I do, however, I was in a similar situation (multi-instrumentalist looking for a 'good' e-kit) just a few months ago and I can tell you what I learned and what I did:
1. Brands: Yamaha and Roland absolutely dominate the market, and with good reason. Some other mfr's make toys and a few make ridiculously high-priced high-end stuff. Most people seem to prefer Roland, but there is a pretty steep price premium to be paid for that. That's one reason I chose Yamaha. I figured it had to be 'good enough' for me, and I just couldn't justify the price difference.
2. Surfaces: Basically there are three choices: hard rubber, Yamaha's textured cellular silicone (TCS), and Roland's mesh. The rubber is generally cheapest, but most people seem to like it the least. So, by default, you're probably going to indirectly choose a brand by choosing a surface. Go to a big music store and play on both the mesh and the TCS to see which you prefer. I preferred the TCS, lucky for me since those kits are generally cheaper.
3. Electronics: This is where it gets complicated. I think most people prefer Roland because the user interface on the device is more graphic and simpler, and they seem to prefer Roland sounds. I'm a computer guy, so the 'simpler' interface was a non-issue for me. Plus, I bought mine primarily for recording with a DAW (like you), so the sounds are also almost irrelevant. I just wanted decent sounds for casual playing, but when I record, I'll use something far superior on my computer anyway. Each company makes many different models with varying numbers of kit sounds, and varying number of trigger inputs. You'll have to figure out what you need vs what is available.
4. USB/MIDI/DAW: Almost any e-kit will do in this regard, if you have any kind of understanding of MIDI.
5. Buying parts vs kits: It seemed to me that you get much greater bang for your buck just buying a kit. Individual parts are pricey, and nobody is going to guarantee you that every individual part you bought is completely compatible with every other part. Even if you stick with one mfr, it could be dicey, across different mfr's - forget it.
6. Alternatives: The Roland SPD's and Yamaha Multipads are a possibility. I wanted the experience of playing 'like a real drummer at a real kit', so I eventually got a Yamaha DTX-562. However, these multipad devices are capable of quite a bit. You might want to look into them.
7. Kick pedal. You're saying you want this:
That is going to depend on the kit, but shouldn't be a problem. Only the very cheapest kits have the "e-pedal".
Are there any decent drum modules that just function as interfaces, donít have any pre-loaded sounds or audio output?
I bought one about 20 years ago (the second OCTAPAD), but I don't think anybody makes anything like that today. No market for it. (I could be wrong)
How quickly does e-drum technology become obsolete?
Good question. In one sense, my 20 year old OCTAPAD is still viable, but the newer stuff is much more sophisticated. It seems like 5-year old stuff still gets plenty of interest on ebay. Even 10-year old stuff is far from what I would call 'obsolete'.
My advice to you would be to first determine what kind of surface you like, rubber, mesh, or TCS. Then go to ebay and craigslist. If you plan on using computer-based sounds, then you probably don't care so much about module-based sounds, and therefore, any older cheaper kit is probably fine. You should probably be much more concerned about the physical condition of everything.