I'm not aware of a program which will batch convert and batch normalise volume at the same time. Best to normalise a batch of Mp3s using MP3 Gain:
http://mp3gain.sourceforge.net/
Then convert them with media Coder:
http://mediacoder.sourceforge.net/
Both programs are fast, easy and free
Audacity is superb, buy doesn't work in batches - single tracks only