Need a psychologist advice about three simple questions

"Visual Music" project is to create a visual music for deaf people where they can have hearing experience through watching sounds. the project will experiment between one deaf group and one hearing group. the purpose of experimenting is to compare between the two groups in terms of the hearing and musical memory influence on their interactions and feedbacks.
My questions are: how many people do you think I need in each group? how old are they and why?
I need please rational answers with explanations.

Please send me a quote for answering these three questions and I will be happy to reply with more details if needed,

Many thanks,
Hala