Can I choose which mp3 should be played in the Arduino code?
There isn't any cheaper solution?
B) 1) An IC (like SpeakerJet) And what should I need for this B option to get it working?
Note that because the Lillypad does not use the same pin layout as a traditional Arduino there is no advantage to getting an Arduino Shield.
For-Seeker: but what do I need with the ICs? What kind of shield do I need to get this work for me?
Or the best question would be: what things should I watch when I search for a good shield to get that kind of IC work for me?