The answer to your first question varies from guy to guy but is generally reported as "not very long".
As to the second question, if you look at the diagram on the right side of the Wikipedia page for "Corpus cavernosum penis
" you will see that the glans is shaped like a cup and the ends of the left and right cylinders of the corpus cavernosum slot pretty far into it (like a shot glass upended over two breadsticks). Your implant fills the same space. Next time you cycle your device feel for the ends of the inflatable rods while you are pumped up. I think you will be surprised how far forward they extend.