the PMP 450m or at least the PMP 450i are the best options. But again, I do recomment also the PMP 450m Access Point. But, beyond 10 Km for example 14-15 Km, if there are other 5 GHz users, you might need the PMP 450i connetorized radio Subscriber Modules to increase the gain or received signal.
And as you evolve, you might be able to have the option to use the 3 GHz PMP 450m Access Point or have more towers to decrease link ranges.
Again, do not align your access using eyes, plan your networks deploy the access point on the planned tower height and use either compass or RF alignment tool dedicated for Access Points.
This will have to know the exact number of access points needs and the right coveraded area.
As clients increase, you might add more APs as one supports around 238 SMs.