Nubie Question

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.

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

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.

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.

I started from scratch a couple of years ago now, trying to produce my own music.  My first attempts at mixing weren't horrible, but mastering was awful.  Ozone 5 helped.  I also acquired other mastering-type plugins - eq's, compressors, maximizers - and I am now at a point where my masters are much better.
 
My latest production is here:  http://forum.cakewalk.com...The-Mail-m3313805.aspx
 
I can elaborate on what I'm doing if you're interested.  Post here or send me a PM.