1) Medium to High Possibility
The bad thing about this case is your friend made a confession. In order to overrule the confession, there must be evidence suggested that the confession did not match the evidence.
Secondly, it will be the evidence itself (the mobile phone). The law authorises law enforcement to search when it deems necessary. But this only includes human. The police did not probably get a search warrant to search an object. (Likewise, a police can't say he needs to search your computer because he "thinks" you have illegal movie in your computer.)
Furthermore, by removing the mobile phone from your friend's possession, it prohibit your friend's right to seek legal advice, unless your friend has been offered to use other phone.
So based on that, your friend has a good chance. But remember, find a lawyer to discuss or use legal-aid.
2) They are not the only one. In fact, if the CCTV can prove your friend's innocence, you can ask the court for issuing an order for the CCTV at the court as evidence.
3) No one knows. The one who used by Nicolas Tse will be a good one.