Thank you everyone, for the micking I used 2 mics: a akg 414 and a beringer c2. There is something abouth having two ears that means that we hear from any sound source certain number of cancelations in the waves, so that's why using two mics should sound more "natural".
The nail thing is go gain some extra strenght, leverage and bright in the tone, higher partials let us get a clearer definition of the pitch. The thing is that you can also play without nails, what you should try to achieve is stoping the string at the moment of the planting, a string slide through the finger (flesh) and nail if any, a very fast atack (planting+preasure and release should be as fast as posible regardless the bpm. If the ramp of your finger/nail isn´t smooth your finger could get stuck, if the release is to abrupt cause a to sharp edge on the nail, or the ramp is too short making the string to snap you´ll get a harch sound. I like to think like this: first planting ( I damp the string, prepare to atack), preasure/ displacement of the string in the direction of the sound hole (because this excites better the top of the guitar), first on my finger flesh (this get us lower partials = body), then the string rides on the nail, and then release the string letting it snap ( the way we want the string to snap).
The movement of each finger comes from the big knucle of each finger but if posible the whole arm should be relaxed and we should try ot take advantage of the weight of the arm.
If you play electric guitar, is the same, specially the direction of preasure of the strings, even you are using a pick Given the fact the amp compress the sound, playing with certain preasure wont make you play louder, but the tone will be different. Remember that electric guitars use magnetic mics, and if you play to soft the gain needed to amp your tone will also amp any extrange noise around. Sorry for beeing that long........