I believe that finding the balance of drones would be putting a limit on how many drones a country can use at one time. I'm not sure on the other 2 questions.
He didnt have the tools, supplies, or time to go farther inland. Plus natives were a huge concern, it was a safer decision for him to stay on the coast so he could retreat to his ship if he needed to.
In 2010 it was approximately 53,364 I believe there is now 92,000
He was elected in D. 1860.
Hope that helped you.