Wireless Intranet

Dear sir,
I want to design an wide intranet over a large area .(maximum distance ia 20 km).
I want to select best solution for network design .
I have enough IP addresses (a C class).
I don’t want to waste it !
In my plan aI have a central siteand some priferal sites .
All of these sites must connected in one intranet for some data transaction and all of them will use internet .
Do I have to assign a valid Ip address to any sites or it’s better to use private Ip addresses ?
This is a big decision and I have to challeng with dozen of people 🙁
I would be very pleased if you help me .
Regard