I'm looking for the manufacturer's recommended DBFS parameters for the plugins to get mixes dialed-in

Thats like saying that each painter's painting was done the same exact way, using the same brushstrokes, paint brushes, colors and painting tools. It doesn't work like that buddy. sorry to burst your bubble. but your ears and knowledge tell you how to set each plugin.
 
Each song will always need different things done to it in order for it to sound the way you wan tit to sound, so what you want is impossible. 
 
Your ears tells you how to set each plugin that you 'chose' to use.
 
CJ

Setting the trim for each track so that each peaks around -12dbFS is probably a good starting point, arbitrary as it is.

Yeah this question makes no sense to me. There's no magic db range that differs from plugin to plugin that if you slalom correctly you'll get the perfect mix. 

MondoArt
Setting the trim for each track so that each peaks around -12dbFS is probably a good starting point, arbitrary as it is.

If you have 40 tracks and each re set at -12dB, they would be clipping!!!! The sum of 1 track is less then the sum of 10 tracks at equal volume.
 
There is no starting point. It all depends on hundreds and thousands of variables.

I would keep all trims at 0dB or unity. Adjust volume using track faders, sends and buses.
 
CJ

I can't believe there's no cheat codes for Sonar!  Every program sold on Steam has cheat codes.
/sarcastica

The +10 ring of perfect mixes is under the blue rock next to the Alder tree in level 4.

Addressing the OP, there are a lot of options but I would advise working backwards from the output.
 
For example, the interface is hardware, so it can't go above 0 without clipping. So you should keep your master fader at 0 or close to it.
 
I generally start off with my channel faders at what would be technically defined as "y'know, quite a bit below 0"  because as CJays Music pointed out, the more channels you have adding into the mixer, the more you need to reduce the individual channels. SONAR's Quick Group functions is great for this because if your levels creep up over the course of a project, you can bring them all down by the same amount.
 
Then you gain-stage within the channel strips (ProChannel and FX bin) to avoid clipping at the input, output, and internally within where the effects live.
 
One fine point is that SONAR's audio engine has a helluva lot of dynamic range. You can usually get away with having all your mixer channels lighting up red like a Christmas tree, and as long as you keep the master down and the channel strips are gain-staged properly, you'll be able to feed the interface the correct level. But that will usually come back to bite you at some point, like it you want to add a hardware insert, do a smooth fadeout with the master fader, etc. So I definitely don't recommend it...but if a channel goes into the red sometime, and you have the master fader pulled back a bit, the mix police will not ask you to appear in court.