I've got mixing somewhat under control; however, I'm still having a problem with mastering.  Are their rules to follow to get that 'radio ready' mix?  Achieving the optimum overall level and eq is giving me a headache.   I want my levels to be the same (or very close) to the commercial tracks produced by (Ed Sheeran, Prince, Earth Wind & Fire, Yellowjackets, etc.).  I don't think my car speakers can take any more sudden volume spikes.

There is no short answer to your question. Mastering is a separate study within itself.
You should search the web for mastering specific information material, post, videos etc.
Check Groove 3 or Izotope (Izotope has a free download PDF on mastering which is good to help start wrapping your head around what is what in the mastering process.

I was told to checkout iZotope Ozone 7.  Will this help me with this dilemma?

Yes. The Maximizer module is what you are looking for to increase overall "loudness" while limiting peaks.
The Matching EQ does a great job giving your mixes that "radio ready" sound. Assuming your mix is good.
 

Word of caution on Ozone 7.
 
If you don't understand the principles of mastering you can ruin your mix with Ozone 7 (or any other mastering toolset for that matter).

Thanks!  You all gave me some great ideas!

I definitely agree with the above comments. Ozone 7 is incredibly capable but also needs a person driving the machine. As with any process, it is not a "slap it on and go" thing.
 
That said... iZotope has nice, free, public documentation on this page. Scroll down to the  "Free Guide: Mastering with Ozone" and check out that pdf. (All of) iZotope's resources there are "sort of" geared to their products, but also written at a very high level that can be applied to any plugins "of a similar type."
 
From a limiter-specific perspective, Limiter No6 is a nice freebie to play with. Bear in mind that many presets (of any application) are often pretty drastic... is fine to start with them, but then learn the nuances (what the settings all actually do). IIRC "Master 1" is the most squashed setting in Limiter No6., so play with settings, but don't "rely" on them.

jatoth
Assuming your mix is good.
 

+1 And what Bapu (Ed) said (and Mettelus).
I believe that this is the first goal. Afterwards it is about nuances, not plugins. It takes time (and a good room / monitor situation / ears / experience / etc) to be able to do the "final touch".
The main thing here (in my mind) is that it takes time not plugins.
But everyone has their own path to follow 
Just remember that it is about the journey, not the final goal (or something like that, someone much smarter than me once said) that matters.
Best of luck.
Edit..
 

I do DIY mastering in Sonar without any extra "mastering tools."  For a single song, it's really an extension of the mix process.  A little compression and EQ on the master bus to glue it all together, and certainly a limiter to bring the level up and chop off the highest spikes.  However, if your mix is good you shouldn't see too much difference in the dynamic range after limiting, provided you're not squashing the crap out of your mix.
 
For an album of songs, it's essentially the same thing, but with the additional consideration of sonic unity across all the tracks.

We are hoping that soon Sonar would include a few more mastering tools like what Wav Lab has for example. 
The most important tool for me is the Global Analyzer which tells you your average RMS level. This is what you are looking for when trying to see where your mix is compaired to commercial mixes. If it is sitting at a peak level of -.05db but the average level is only - 17 db then you need to either go back to the mix or squish it in a limiter. I like the multi band limiter as it leaves dynamics in the upper mids and mostly squashes the low end which is where most people have mastering issues.