...I'll try to help.
For real mastering a good wave editor is nice to have. You can get Adobe Audition 3 for free. It can do so much, I'll leave it to you to google eveything it can do. I use it to edit peaks all the time. That helps reduce the work a compressor and limiter have to do later.
A good free cd burning program is good to have. I use CDburnerXP.
One of the best limiters available (IMHO) is free. LimiterNo.6 by vladg sound. He now works for Tokyo Dawn.
One of the very best Bus compressors is free...Kotelnikov by Tokyo Dawn. Get everything they have for free. They make awesome plugins!
Remember a project happens in steps...
1. Recording
2. Mixing/editing
3. Mastering (usually referring to the entire project or album)
Sonar excels at the first two, but since you can't insert cd markers your reduced to exporting each song and reassembling them in a cd burning program or a wave editor that can insert cd markers. Sonar can master songs individually, just not as a group.
Programs like Ozone and T-racks are great, but they are not wave editors. If you want one song to cross fade into another you will want to get an editor. There are others that are free (audacity, wavosaur), but I prefer Adobe Audition.
If you don't need to do cross fades (I rarely do) the one at a time approach will work with Sonar. You can create a project and import your mixes on separate tracks and balance the levels and eq...then export them. This is what Ozone and T-racks does.
Hope that helps. If you need any help finding these programs or if you have other questions...let me know.