Just a comment on why you're converting your music to wma... The statement "it can fit twice as many wma files on it as mp3" leads me to believe that you're assuming the mp3 player can only fit a specific number of files, but this is incorrect. MP3 players come in different sizes of storage (mega/gigabytes) and the number of files they store is only dependant on the size of the file. If you have the same size mp3 and wma files then you will be only able to store the exact same amount of both kinds.
The "it can fit twice as many wma files on it as mp3" statement is often used to try convince people that wma as a half decent audio file. In order for this statement to be 'true' you will need to encode your wma files to a lower bitrate (and hence worse quality). So would you rather a lot of bad quality audio files, or some good quality ones.
You can also encode your mp3 files to a lower bitrate and achieve the exact same result, so a "it can fit twice as many mp3 files on it as wma" statement can be made for this. The only reason you don't see these around is because mp3 doesn't have a multi-billion dollar corporation funding its media campaign.
When it comes down to it, I would much prefer the mp3 format over the wma one simply because of the copy protection (which causes soo much hassle) that can be placed into wma files.