With regards to downloading, I believe Homecoming still uses what was implemented in Legacy, so it should download and install in stages. I say should, but I didn't test this when I first installed this last year.
1st: Character Creator - You should be able to launch and enter the CC while the rest continues to download.
2nd: The tutorial. If you wish to play through the tutorial, you should be able to enter that after creating your character, depending on how long you spend mucking about in the CC.
3rd: Atlas Park/Mercy Island/Nova Praetoria - The starting zone should be accessible next.
4th: The rest of the game.
At each stage the installer should tell you that the next section is available.