It's ready to go out the box which is very handy. I bought a 20 metre hose off Amazon for £13 I think. That's fitted to one of the outlets for using outside the workshop and the coiled 5 metre hose that comes with the compressor is what I use in the workshop.
I can't really answer your question accurately about it filling back up after running. For example, I can use the air gun to clear out dust and gunk all day before the compressor needs to top back up. But using the tyre inflator it'll kick back in much more quickly. So it really depends on your application.
I'm also not sure about the oil. The instructions are good and fairly comprehensive though so I'm sure they say something about it.