We do not have any definite instruction from the Prophet (pbuh) detailing how to break hands in Witr prayer. If you do your Witr prayer in one go then you may or may not say Takbeer at the start of every odd Rak'ah. If you read every two Rak'ah separately before reading the last one then obviously you will need to say Takbeer at the start of each two Rak'ah. As for Niyah, it is enough to know what you are doing. This is all that Niyah means. It does not need to be recited or to be mentioned in your heart. Please read the following link: How to Offer Witr Prayers Answer published by Abdullah Rahim