What exactly do you mean by "running processes"? I don't think I've ever seen a Unix with only 1 to 3 running processes in total, so you are probably referring to processes in a certain state. Runnable (R)? Uninterruptible sleep (D)? Both? Something else?
Just that, 250-300 running processes in top shown for a second. 250-300 is the number of postgres worker processes used, but normally only 1-3 of them are running according to top. At times of load FreeBSD (?) schedules all of them to run. This doesn't really put the machine on its knees, it just impacts load avg.
