I can answer the first question. The "wall" you run into, is actually made by you. Yes, you. When I first begun practicing, I was kinda freaked out by stuff moving by themselves.
So whenever I successfully pushed something, the object had a habit of suddenly stopping dead in it's tracks defying all known laws of momentum, and afterwards I was unable to move the object at all. Like it was "frozen" in space.
It took me a while to figure out that it was me who was freezing stuff. Objects not moving=>nothing creeps me out=>my reality isn't crumbling.
It still occasionally happens, but if you practice long enough, you'll probably get over whatever makes you "freeze" stuff. Maybe for you it's something else that triggers it.
On the other hand, this technique can be useful, when you use it conciously. If you get strong enough you can put things in a mini "stasis".