In regards to AA, it's usually just case by case basis. If you over-AA, often the piece becomes blurred looking, even pillow shaded in some cases. Or just not as clean and readable as it should be. That's why the right version 'pops' out more. The solid black outlines contrast with the shades and then the highlights on the edges. However, the solid black doesn't always look good either; try to work with a mix between the two for really nice isometric work. Use black where you really need it, if not, use a darker shade of the object's colour. You will just have to learn to judge which is better looking.
That aside, if you plan to add characters and objects that you want to stand out, then it's not such a bad thing that the building looks a little dull or blurred, then characters with dark outlines and bright colours will stand out really nicely.
In my opinion, noise doesn't add anything to pixel art. And at it's size, those bricks don't need to be individually personalised. But it's really up to you.
The size of the steps should be defined after you know how large the characters will be. Otherwise, there is no comparison. You can't see whether your steps are too tall or short until you see a character next to it, or an object.
