Sentence 3 ("You have to walk up for...") sounds the most awkward to my ear. All of them seem improper, but could be found in colloquial speech such as giving directions. I also read all of these in a southern American accent in my head, but maybe that's just me.
Anyway, to answer your other questions, no "up" does not imply "north". If the street is sloped it could imply walk uphill. If you are already on Elm street and someone says "Just go up the street another 200 feet" it would imply continue in the direction you are already moving. Otherwise I'd expect it to be accompanied by a hand gesture, more words, or both ("At the Elm/Main intersection take a left, then walk up Elm St 200 feet")
The most natural directions heavily depend on the situation. For example, where I live now thanks to some unique geography most people know which way is N/S/E/W instinctively, so saying "walk north another block" would be a good direction, but in my hometown I would rarely know which direction things were in without consulting a map.
I think the most fool-proof way to give directions is to say things in multiple ways, including left/right directions and blocks when possible. For example:
The gas station is a few blocks north of here, so you can walk that way (gesture) 2 blocks to Elm street, take a right turn and go straight for 200 feet. It'll be on your left"
If you aren't there at the time, I'd try to use landmarks to explain your point
If you're on Main street facing the high school, walk to your left 2 blocks...
Or always the tried and true
Just put it into google maps and let it tell you