with all due respect, if you cant hear the difference between what is happening to a mix through a SSL VCA limiter, a variable mu tube limiter and a digital limiter you either arent listening hard enough or your monitoring should come into some question as those three boxes are about as different from each other as they can be, sonically speaking.
The way to use any piece of gear, regardless of what it is, is turn the knob until it sounds good to you. Any advice you get beyond that is fairly worthless from an engineering standpoint as any decision you make with a limiter *always* is dependant upon the material you are feeding it, how that interacts with the limiter and of course what your expectations are and what you are trying to achieve. you could put one of 15 different limiters on your mix buss and none is more right than the next, it comes down to what you are trying to do as an engineer and what the song will allow happen. Use your ears is the best advice you'll get on the subject since ultimately, its personally subjective.
If your mix sounds better with the buss limiter and another limiter in series, thats what you should do, you are the engineer, its your call. When you say "final master" exactly what do you mean? If you are comparing your results on your console to any commercially available music mixed on the same desk, do take into consideration that regardless of how that mix was handled coming out of the console, it still went to a mastering engineer who in this day and age, probably compressed it a touch and definitely limited it, so all the commercial stuff you hear that was done on a SSL has plenty of additional compression happening in mastering.
A good setting to also consider on the SSL limiter is the "off" setting. The biggest mistake I have seen people do is turn on all those channel limiters just because they were there, be selective about what you compress. Some songs that buss limiter might be awesome on, others it might not be the best thing in the world, dont feel obligated to have it on just because its there. the songs usually will tell you what they want if you pause to listen to what they are telling you.
hopefully this is helpful, Im not trying to be a smart ass.
dave