The driver will move the stepper one step each time the STEP pin transitions from low (0V) to high (3-5.5V). Also, ~1us is the minimum time the STEP pin needs to be held in the HIGH or LOW state to register, but much slower pulses (like several milliseconds) can work just fine, too. In practice, there is not much reason to use a pulse below 10us.
Many of your soldering joints still do not look like they would make reliable connections. What kind of solder and soldering iron are you using? Did you look through the "Making a good solder joint" section of that Adafruit guide I mentioned? If you look at the picture for the "Heat the joint" step, you will notice that the tip of the iron is in contact with both the solder pad on the PCB and lead of the component going through the board. Heating the pad is important so that the solder flows on to it as well (many of your joints do not appear to have solder on the PCB's pads). Having the tip of the iron wet with just a little bit of liquid solder before touching the iron to the joint can help the iron transfer heat to the joint.
Also, the amber colored material on your joints is soldering flux and you might try cleaning it off with some isopropyl alcohol and an old toothbrush before attempting to retouch them. After a while, flux can build up like that and make things more difficult.