I think that we will likely be able to walk around on ship and stations. The pictures from the inside of the Courier are explicit enough.
(...)
I would like to get the planet landing too, but I think that we never see this feature in the currently purchased game.
I think you should aim lower for that one.
No walking around or landing before expansions, though those will come. Powerplay/1.3 is a free update and the Newsletter puts it clearly as such :
And of course, Powerplay is a FREE content update for all Elite: Dangerous players and will be part of Elite: Dangerous for Mac and Xbox One at launch.
I could go find at least one image from a python cockpit taken from behind the pilot seats, walking around ship wasnt planned for gamma though.
They can move the camera around, they developped that game after all. This is only to give you a feel of the final thing. But we will still have to wait, and once we're there, we'll know. This is far too early.
As for thargoids... i couldnt say, but i feel it's a tad early for that too. Though i could be wrong there. I dont know if FD would put them in game without a word.