I believe so. If a Vocaloid song is fanmade, then i think so. A vocaloid singing a previously-copywrited song, though... I'm not sure, it's probably illegal.
Live mixtapes.com
Youtube
You can not LEGALLY download music for free.
No. VOCALOID 2 is a software that you need to pay for. If you are looking for the free version of VOCALOID 2 then use Utaloid. It was made by fans and is free.
Vocaloid is a program used to simulate a human voice for use in songs. Hatsune Miku is a popular Japanese Vocaloid.
You can download songs by going to the iTunes Store.
You can download IA Vocaloid songs from Nicosound. This site is basically the audio version of NicoNicoDouga. On this site you can download all of IA's songs that have been posted on NicoNicoDouga.
beemp3.com
Yes
In Spotify.
When it comes to downloading songs, words "legally" and "free" don't go together. Either pay for it or download it illegally. Or don't download it at all.
Teto's character item is, apparently, french bread. Note that Teto Kasane is not a Vocaloid, but an Utauloid for the free singing synthesizer UTAU. Since the Vocaloid and UTAU communities are closely related, Teto and other UTAUloids have many fans within the Vocaloid community and its not surprising to see many songs featuring Teto or other UTAUloids singing alongside their Vocaloid counterparts.