It sounds like you are on the right track!
It helps if your cows are just intimidated enough by you to respect your space and not crowd you. Cows being a herd animal, they very much have a pecking order and bigger, older cows will push around the smaller, younger ones. Unless they recognize you as the dominant one, they will try to push you too (say, to get at the bucket of feed you're carrying) and, because they're so large, you can inadvertently get hurt.
All my animals know what "Get back!" accompanied by a clap of the hands means. (Doesn't mean they always obey though!)
If your cows get pushy, you can carry a lunge whip (the kind used by horsemen) and use it to enforce your space. These whips are really handy when working with a large number of animals. (You don't really use it as a whip, more like as an extension of your arm to direct and block.)
Be aware that, much like horses, cows will be sensitive to your body language. If you're trying to drive a cow forward, stay behind her shoulder. If you get too far out in front, she will balk or turn. If you're trying to get a cow through a doorway or opening, and she balks in a major way, you can get behind her and press her tail against her back end, or even fold it up a little to put pressure on her to get her to move. This is sort of the last resort though. Remember that cows are prey animals and they're naturally looking for the wolf behind every rock. When I have to get a heifer in the parlor for the first time, I get her going in the direction of the doorway, but the closer she gets, the more I back off. I try to deliberately "relax" to show her there is nothing to be afraid of. I let her stop and sniff the doorway and look around. Especially if there are already cows inside, she'll usually go in on her own once she's satisfied her curiousity.
Now, about the halter thing! Easiest thing to do is make a rope halter. You can probably Google directions, but let's see if I can explain it.
Take a good long piece of stout rope. Take one end, fold it over, and tie a knot so you have a loop (not a slipknot) in the end. Then run the opposite end of the rope through the loop so it makes a circle. This goes around the nose of the animal. Then, take the long end of the rope, run it up around the poll (behind the ears) and through the circle, on the inside or closest to the animal, on the other side of the nose. Loop it back through the circle (NOT back around the poll) once or twice. Ta-DAH! A halter and lead rope all in one! You can even take a separate little piece of rope and make a chin strap to help hold it place.
I am sure you can find a diagram that will explain it much better than I just did!
The nice thing about a rope halter is that when you pull on it, it puts pressure on the poll, which is a fairly sensitive area. It also releases pressure much more quickly when an animal obeys by stepping forward, which is a reward of sorts. So it helps condition the animal to being led.
