Hello, my name is Rusty. Yes, a limiter is part of mastering, it's more of a compression unit with a limiter. It allows the frequencies to hit a ceiling before being stopped, so that the audio goes as high as possible without clipping. There are tons of programs out there, Pro Tools with Bluecat is what I use for mastering, but you shouldn't have to worry about that. Your DP32 has a mastering program built in.
Click here and look at page 15. You already have the hardware and software to master your recordings.
Ok, I've had that problem with the all in one recorders as well. Click here. I am showing you this one because it's a platform, not a plugin, so this is all the software you will need. It also has a free trial. With this software, you can listen in real time, dial in your parametric EQ, then use the maximizer to get the most volume out of your songs.