The general understanding of vibrato is that it is a fluctuation in pitch, whereas tremolo is a fluctuation in volume. For tremolo, I use the LFO to modulate the filter or the amplitude. I've found that modulating the pan spread also works.
Now for the strings! I've found that a patch using all sawtooth waveforms makes for a stiff dry effect, and all PWM makes for an unpleasant overly electronic effect. So, I mix the two together. I set the PWM at a deep level and a rate of between "16 and "26" (on the Prophet '08). My standard is to use as extreme a depth and rate as the lowest note in the piece will allow, while still being musical. As for tuning, I spread the oscillators as far as "10" above the main oscillator and perhaps "5" or "6" below it. It's commonsensical not to tune in only one direction, so that the instrument doesn't get far off the pitch of the other instruments. I always use vibrato at a depth of perhaps "2" and a rate of between "64" and "72." As for the envelopes - it depends on the music, on the speed at which you'll be playing. Generally, I'll use a moderately slow Amp Attack, combined, with a somewhat slower filter Attack and a slow decay back to "0." This adds a slight dynamic bowing effect. Lastly, in order to add an organic heaving effect, I modulate the filter very slightly and very slowly. This adds a wonderful breathing human-like effect to sustained chords.
Those are my secrets. One more. Everything is duplicated on a P'08 module and keyboard and module are panning to opposite sides. This makes all the difference in the world. And the two instruments are detuned by 2 or 3 digits.