We have audio mp3 files form various people with various volume levels, and the Limiter seems to bring everything to ceiling/thresholdDb to 0 through a default use. Is this correct?

The best would be to analyze each mp3 file for it's average and peak decibel values (using SuperpoweredOfflineAnalyzer for example). Then adjust the gain (volume) of the player to a default average loudness value (such as -11 db), and if the peak of the file goes above 0 db, use the SuperpoweredLimiter.