I think the stats on the wiki are correct:
https://www.realmeye.com/wiki/soul-s-guidance
One thing not mentioned there is the damage seems to be armour ignoring (shown in purple in game), like Assassin’s poisons. Also like poisons the damage over time keeps going even if an enemy goes invulnerable.
There doesn’t seem to be a limit to their number. Insteat it’s naturally limited by your fire rate. On average you should have 15/100 × (shots fired in 5 seconds) alive, after 5 seconds, and it doesn’t vary much.
I think each gets its own chance to do damage, so the more you have the more damage potential there is. Potential though as they move erratically and there’s little you can do except get close enough to targets. Also the damage is against a single target, so in a crowd it could be spread out, could even be wasted on minions with less than 500 HP.
Except perhaps the final explosion which the wiki says is area effect and is when it curses things. But this, after they’ve been alive 5 seconds and started drifting off, is very unreliable. Chances are by the time it happens most small things that would be wiped out by an area effect are dead already, so it just works as (delayed/sometimes) curse on the big bad that’s still alive.