My general rule of thumb on springs is how often does the player use the vibrato bar and what
gauge strings does he have? Then i decide how many springs to use from there. For a non floating floyd ala, evh axis, wolfgang, charvel, older kramers, two springs are often ideal to get that floating feel out of the bar, i still prefer 3 personally myself but ive known of evh and other cats to only use 2 on a nonfloating tremolo.
ON
floating bridges i always start with 3, for gauges 8 and 9, ill only add a 4th spring for 10's if the springs are too open, or i run out of rum on the tremolo claw. Imho 11's and up in standard tuning work much better with 5 but, its more common nowadays to have people using those gauges tuning way down so make sure you match the tuning with the amount of tension you need.
*looking back over that it looks like some mad rant but i think you get the ideal from the post*