Hi, and welcome to Arduino.
You'd have to create a huge hilt to get an Uno in, so your other choice would be better.
The MP3 module isn't an MP3 module, but an audio playback module.
The difference is in the MP3 file format, which the WTV020SD doesn't seem to support.
Instead you'd need to convert your files into an other format.
And you need to connect some kind of speaker to it.
Read this huge thread a few times over your Christmas holidays.
There's tons of details in it.
You'll need batteries, and a Lightsaber isn't a Lightsaber if there is no light.
So that's something to take care of too.