Why always the singe direction push Scepti? If I walk horizontally and displace air, why am I not pushed back to where I started? Or if I walk down a steep hill, why am I not pushed back up?
Let's take a mild day, no wind. Your body has already displaced the air you are standing in. We can agree on this, right?
Until you move, everything around you is equally acting on you, as in atmospheric pressure. Because you are stood upright, you have the air pressure bearing DOWN onto your head and shoulders, withe the rest distributed around your body from the sides. The soles of your feet are being pushed to the ground with the ground resisting that push from above. All the pressure is absorbed up your muscles from that point all the way up to the last muscle in your neck. Bascially you are being compressed but are strong enough to resist it. You are much stronger than you think but you don't appreciate it because your body is naturally geared to the environment it's in. You only realise how strong you are when you see the pressure difference when you try to evacuate it at sea level and realise the actual push on you from all angles.
A window clamp (known as a suction cup) is a classic example of the push exterted onto anything. What keeps that cup to the window is what keeps your feet pushed to the ground through your upper body.
Because your body is strong and long, you can walk horizontally against the pressure due to your huge surface area pushing it out of the way...but the second you do so, you force that air around you which will leave a lower pressure behind you, until that pressure you pushed through, comes around you and from above to fill it which is always trying to create a push back onto you which keeps you in balance but not a complete perfect balance because although it's always playing close catch up, it cannot smack back into you...UNLESS you make an abrupt stop, which only then will you feel that force, which if you pay attention to bodily motion, you will see a person stop dead and then be pushed forward slightly. This is the catch up.
No action, no reaction. Action must come first before any reaction can start. It's why people are under the misconception that friction is a pain in the @rse to movement, when it's all relative to movement. You simply don't move without it no matter what energy you use in whatever form. This is why space rockets do not work but that's been debated, so forget about that.
If air pressure is equal from all sides, how does it know which way to push me?
It's not about it knowing anything. You effect it or any object within it. As above explanation.
Also, a total and complete vacuum is possible if air molecules are interconnected and change size (like bubbles) with a simple vacuum chamber according to your hypothesis.
A total vacuum on Earth is absolutely impossible. There's no argument to this. It is literally impossible. A large evacuation is possible and that's it. If you make a complete vacuum, you end all life in any form.