To concatenate the MP3s to an M4B, you could use ffmpeg. Download a recent version, then run:
ffmpeg -i "concat:input0.mp3|input1.mp3|input2.mp3" -c:a libfdk_aac -b:a 64k -f mp4 output.m4b
Your ffmpeg might not have fdk_aac
enabled; if that's the case, you can try using
-c:a libfaac
(high quality)-c:a aac -strict experimental
(decent quality, but use higher bitrates)-c:a libvo_aacenc
(rather bad quality)
See the AAC encoding guide for more info.
If you want to use neroAacEnc instead, you could use:
ffmpeg -i "concat:input0.mp3|input1.mp3|input2.mp3" -f wav - | neroAacEnc -if - -ignorelength -q 0.3 output.m4b
Neither of these will add chapter metadata, I'm afraid.