Gollum questions.

[Legate of Amon Lanc]

I would say all of your questions are more or less exactly the same as the ones Gandalf answers to Frodo in the second chapter of the Fellowship of the Ring. Especially your questions 1, 3 and 4 are the ones Frodo asks him, or implicitely asks him, and Gandalf replies precisely these exact questions. I think the book, or Gandalf, answers it much better than anyone here could, because if you paraphrase it, you're certain to leave something out.

Your question #2 is effectively answered too, although not as openly... the main trouble comes, I believe, from understanding what one means by the term "Hobbit". If by "Hobbit" you understand only the Hobbits from the Shire, then obviously there is a difference. But effectively, there were the halflings - the Hobbits - who had three branches, one of which were the Stoors, and another were the Harfoots (the Shire-Hobbits). Imagine it the same way there were several kinds of Elves: the High-Elves (Noldor), the Grey Elves, the Wood-elves... yet all were Elves.

The differentiation of the Hobbits into several groups happened only a couple of thousand years before the War of the Ring, so I think you can't even think about the distance similar to Neanderthalians and such.