1-Should i limit myself to mono channels for instruments and then on the mix down, create a stereo file with the mastering tools?
(This is because of phase cancelations, and other weird effects that usually makes my work go down the drain..)

Drums should really be mono - unless you've got a really special stereo loop that adds loads to the track. But stereo synth sounds for trance are what makes things really interesting....

NO - don't use stereo mastering for tracks. If you don't 100% know what you're doing, you can make the stereo field too wide which makes it impossible to cut to vinyl.

2-When i need compression, should i compress each instrument individually, after sequencing (like the bass, the kick, the snare, the hat, and all the synths and effects im using), then compress the whole mixdown again.. or just compress them one time all together? what procedure should i use?

Compress as much as you can - as much as your cpu will allow. usually i do the track with a compressor on the main outs then after i've done the whole sequence, put as much single compressors on as many channels as i can until the cpu is maxed out. important sounds to put compression on are kick, bass, snare, crash and synths i reckon.... understand exactly what compression does and why to apply it. read up as much as you can.

3-What tricks should i use to make the instruments sound like they are all in different places in the same room (in the mix), without having the feeling they are on top of each other? Is this related with mono?

Reverb and eq.

4-How important is the use of reverb and chorus for the instruments, individually? Should i use reverb for each one, or reverb in the mixdown?

Very important!!!!! It's essential to consider reverb for each channel. A touch of reverb on the main out can also add a nice gel to everything...

5-Mastering is becoming easier with time... but without a proper mix, it can't do miracles.. What are the crucial steps i should follow in order to make the sound earth shaking?

Research, read and learn. That's all I'd recommend. Read as much as you can about production. Experiment. If you want this man, you'll spend every single hour understanding what you're doing wrong.

Good luck..