Crikey, big old can of worms there.
Mixing is as much a philosophy as a technique, and opinions vary.
My personal philosophy is that the best kind of EQ at mixdown is no EQ.
All EQ is effectively "damaging" the sound in some way.
This follows the classical music method, where each instrument sits in it`s own place "in the mix".
Tubas and Trumbones play the lows, trumpets the mids, violins the highs, for example (vastly simplified).
How does this apply to techno?
Well it begins at composition.
As you are making your tune and adding elements, don`t add them willy-nilly, look at what you have in the mix already, and work out what space you have left in the mix.
If the bass is already covered by kick and bassline then look to add instruments (and melodic parts) that sit in the mid to upper areas.
Working like this means you have to apply less EQ to sounds, (or use it less harshly), so your mix ends up sounding more "natural".
Of course it is best to subtract with EQ rather than add, but you can also boost in some cases, just be careful and again, pay attention to the space left in the mix.
A lot of techno is overcrowded, too many ideas and sound in one mix.
Look at your sequencing, if you absolutely must have that final 5th percussion part at the end of the track, look at where it sits in the mix, and when it comes in maybe take out another instrument that sits in the same place.
Now another thing to look at is stereo field (and also mid/side placement, which is very interesting but a subject in itself). An orchestra is "mixed" by the type of instrument playing and also where they sit in respect to the conductor.
Use the stereo field to also create space in your mix, but don`t overdo your panning, techno is inevitably played on a mono soundsystem, or maybe stereo set up with little consideration for placement. So extreme stereo might well sound shite in the club.
Volume wise, on your channel faders it is generally good practice to keep your levels down, simply because add you add effects and more instruments you will naturally start to push levels up, so you want some "fader play" to allow easy mixing.
Be careful of the signal between plugins, as mentioned above, your DAW has massive headroom, but some plugins don`t, so be careful to check in and out levels of your plugins, and if you can`t adjust them, get a fader plugin between your vst`s. Sonalksis do a good free one.
No I wouldn`t say you use compression on every sound at all.
Use compression on things that you feel need it.
Compression changes the relationship and difference between the quiet and loud parts of whatever is run through it.
You can add or take away punch, increase loudness and control levels with it, but not all sounds need it.
If you don`t know what it does, don`t use it until you do as you can end up ruining a mix.
Limiting is basically extreme compression, so again, you really need to understand its application, and the reason why you are using it.
Its definitely potentially more damaging than standard compression so not for common use at all.
An average decent mixdown will sit at around -14 to -18 RMS before mastering so don`t worry if your mixes sound quiet, it`s to be expected.
If you need to bring them up just for personal use (ie no professional mastering)
Then a combination of a clean compressor and limiter shaving about 2-3db in gain reduction on each should give you a fairly decent final level without totally butchering the thing to ****.