Have a look at DBPowerAmp, it will handle all you need in one package, plus downloading your MP3's to your MP3 player
I use it for all my conversion needs, and its free
http://www.dbpoweramp.com/
To get near CD quality you don't really want to go less than 128k, some say 160k, but no doubt everybody has a preference
If you're listening with the headphones that come with the players, then I suppose you could push it to maybe 112k, try it and see what you think
If you really are desperate to get as much as you can and are not 'too' bothered about the high-end quality, try really pushing to 96k or even 64k, but that may be taking liberties as quality will seriously be effected by then, especially 64k
Try it and see what you think by actually listending to the end result via your player once converted to that rate
Start with 128k, then 112k, 96k and finally 64k if you;re really desperate to squeeze as much as you can on it
With 128k bitrate, you should get at least 2 full albums on the 128MB MP3 players. Ita ll depends on the album total playing time. The longer the total playing time for each album, the less you will get on an average 128MB MP3 player
An average should be at least 2 full albums, if you have an 256MB player, you're looking at about 4-5 full albums at a bitrate of 128k