Forgive me if this is a stupid question...How were the electrons "packed" onto the wire? It was my understanding that metals behave like an electron sea, where when one more electron is introduced, another will flow out the other side. Perhaps this is too simplistic? I find this fascinating.

As pointed out by @lemouth, please cite your sources. Appropriate citation is essential to good scientific discussion. We all use materials written and thought up by others when talking about science, its a field where we all stand on the shoulders of giants. No shame in reporting and citing information.