FFMPEG – Create a video from an image and multiple audio files with an audio transition

I have one image file and multiple audio files and would like to create a video output where the audio files transition smoothly into each other.

I can do 1 file and 1 audio at the moment with this:

ffmpeg -loop 1 -framerate 1 -i image.jpg -i music.mp3 
-c:v libx264 -preset veryslow -crf 0 -c:a copy -shortest output.mkv