IPv6 confusion

Hey everyone (first post) I’ve been studying IT for a short while and just started work on IPv6 on cisco routers.

Don’t suppose anyone can give me a few minutes of their time? I’ve got a whole book of these kind of questions but a head start with this one would really help.

I need to create a IPv6 design for the requirements of at least 300 networks but no more than 65000 networks.
Then I need to figure out the most appropriate prefix? (I think /50 right? or /55?) and the network address, Prefix, gateway and first host address for the first 5 networks