You can put as many new files as you want in /system/media/audio/ringtones - you don't have to remove old ones. Once you put them, reboot and the new ones will show up in picker.
They can be MP3 or AAC as well - not necessary to convert to ogg, but doesn't hurt
Wow, you're right.
For some reason I thought new files wouldn't appear, I guess I didn't reboot the system after putting them there.
Thanks for the info