Chevy
Also, to the others, I appreciate VERY MUCH the comments, but for some reason I don't believe that the modest plugins I have are necessarily the right way to go...  even on a budget. They may be, but... I just don't know right now... There are a buzzillion products out there, and some are definitely just plain better than others. They sound better, they're easier to use, etc.

 
As a self proclaimed "noob", don't get caught up in the game of upgrade after upgrade. You will soon realize there really isn't that much difference between what is bundled in Sonar and a high end plugin. It's an old saying "you pay 95% more for a 5% increase in quality!"...
 
The tools are in Sonar... learn how to use them to the fullest. Once you actually "know" what is missing, you can go buy that product without wasting hundreds (or thousands) trying to figure it out.

Chevy
Also, to the others, I appreciate VERY MUCH the comments, but for some reason I don't believe that the modest plugins I have are necessarily the right way to go...  even on a budget. They may be, but... I just don't know right now... There are a buzzillion products out there, and some are definitely just plain better than others. They sound better, they're easier to use,etc. You can have an eq that's so complicated, even though it sounds good, and is economical, that it's just not worth the effort and time. I'm hoping to narrow down the field so I don't have to waste time sorting out what's worthy and what's not.

Firstly, the plugins that come with Sonar are not "modest". By and large they're as 'good' (or 'bad', these things are very subjective) as many, many others. The same can be said for the plugins that come with most of the long established DAWs. It's not so much that one plugin is 'best' and another 'worst', it's that after a certain point and sufficient experience you might decide that you feel the need for a particular sound, or a particular effect, that you don't have.

But to get to that point you first really ought to be very familiar with what audio processors do and what the characteristics of any particular category, e.g. "compressors" or "eq" or "chorus" or "delay" actually are and what makes one different to another and why those differences might matter. Which means being familiar with what you already have. And not relying on presets but learning how to set them up yourself.

It's easy to drown in plugins, there are so many, and it's a trap best avoided.

Since you mentioned CA-style compressors and limiters, Cakewalk's own CA plugin and Concrete Limiter are extremely good and hold up well against any.

If you really want to stir up things start talking about hardware.  Makes all the difference in sound quality and is very expensive in comparison to software.  Much better way to start an argument.
 
;-)

What you have now is probably sufficient. An important related aspect is understanding what a plugin does, since that individual type has "common components" that will apply to them all (some plugs are "hardwired" for certain elements).
 
An example would be a compressor - knowing when to use it, why to use, and how to use it trumps out nitpicking this compressor versus that compressor. That knowledge is paramount to learn... having the "best" (which is a subjective term anyway) means nothing if you cannot properly use it.

Just as an aside, if you do have spare money burning a hole in your pocket, look at other aspects of your studio before spending on plugins which might, or might not be what you want.
 
Look at your mic locker, room treatment, monitors etc.
 
Upgrading in these areas will make an immediate and significant difference to your music.

Bristol_Jonesey
Just as an aside, if you do have spare money burning a hole in your pocket, look at other aspects of your studio before spending on plugins which might, or might not be what you want.
 
Look at your mic locker, room treatment, monitors etc.
 
Upgrading in these areas will make an immediate and significant difference to your music.

I agree totally And there is no update required if changing OS

+1 I agree, Cakewalk provides a great bundle of mixing and mastering stock plugins.  Also for the price, Computer Music magazine (CD included) has some other nice options.  I like the limiter currently included, Barricade CM.

Bristol_Jonesey
Just as an aside, if you do have spare money burning a hole in your pocket, look at other aspects of your studio before spending on plugins which might, or might not be what you want.
 
Look at your mic locker, room treatment, monitors etc.
 
Upgrading in these areas will make an immediate and significant difference to your music.

This could be the best advice you've been given. If you have the money, don't buy plugins, treat your room.

Pragi
I think for the start you have already a nice arsenal of good plugs:
The PC La2a is a beast -
The PC Eq is good working-
VC 64 -great for vocs
PX 64 - great for drums ......aso asf
if you need more "colours" you also have the nomad BT stuff.
 
If you have registered your focusrite 2/2 interface,
you can get get the red eq and comp for free.
The sonitus plugs are imo a good and neutral sounding
starting point  .
Have fun

Hmmm...  thanks for the hints, but don't see a PC La2a (what's the PC stand for?),  dont' see a PX 64 either...  only one of the four first ones I seem to have is the VC 64...   

To be Honest, Mixing and mastering is basically about the use of a few plugins only.   If you use the plug-ins that came with Sonar and familiarize yourself with how they work, you will have half of mixing and mastering done correctly.  The other half depends on how you use your plug-ins.  Will you mess up the mix for mastering, or will you develop a solid mix and master with what you are willing to learn about the proper use of the plug ins you already own.
 
You decide
 
Here is a great "SoundOnSound" magazine article about the fundamental of Mixing.  Take a read and then see if it's the plug-ins or is it you.
 
Fundamentals of Mixing Article