You can do it with Sonar but myself I would use a wave editor as that's what they are designed to do,,, edit waves.
Example Gold Wave, it's free to try and it has a real good batch convertor so when your done splitting the file into wave files just batch convert them to Mp3, takes a half a minute.
http://www.goldwave.ca/ There are a few other free editors like Wavasour and Audacity but Gold Wave is my favourite. I personaly use Wave Lab elements for this stuff but that's $90.
Always work with a copy, make a back up of your tascam file, or just don't delete it from the SD card.
Now open that file in Gold Wave.
Cutting the songs is simply a matter of highlighting and deleting the rest of the file and just keeping the part you want. You then use Save as , name the song now go back hit undo a few times to bring back the parts you deleted, and carry on. The other way is to copy paste the part to a new blank file. In Gold wave as example CTRL+ N opens a new project.
There are keyboard shortcuts for cut and copy and paste etc that speeds things up.
Doesn't take long to learn all about the software, it's very logical. a lot is done with just draging the mouse and right clicking to bring up actions.
To do this in Sonar you do the same cut and paste or cut and delete but it involves a few more steps and you always have to export. I find wave editors do the job faster and with fewer steps.
Also not sure why you want to go to MP3 right away. I keep everything as wave files and then make a MP3 folder to use just for internet stuff like posting to soundcloud. Much easier to work with wave files. most editors are working in wave format so best leave things alone until the songs a re "mastered"