How hard should you strop? Not too hard, actually, nor do you need to hold the strop extremely taut. Here's a way to limit the amount of force you use, as you learn to strop. It's also a good approach to nondestructive learning, as it's unlikely you'll damage a blade this way, and it won't matter if you damage the temporary strop.
Tear off a quarter of the total width from a newspaper page, put a bulldog paperclip at one end, and hang it from something at about elbow height. Now strop on it. If you pull it from the clip, either from lengthwise tension or from the actual stropping, you're stropping too hard. If you flip too soon, you'll nick or cut the paper--so you may want to wear a leather glove on the paper-holding hand, in case the blade comes for your fingers. A premature flip will nick or slice a real strop, and that will be sad. Not as sad, though, as sliced fingers.
From the sound of blade on paper, you can tell if both the spine and the edge are riding the surface as they should. First, try stropping just the back of the razor--it will be nearly silent, since the back is usually polished smooth. Next, try stropping with the spine on the paper and the edge lifted a couple of spine widths. You'll hear a louder pass, but it will still be the sound of a single surface on the paper. Finally, lay the blade flat and draw it, spine leading, the length of the newsprint. This loudest sound is made by both surfaces (the spine and the edge) in contact with the paper. If you lift either the edge or the spine, you'll drop back to a quieter stroke.
Keep it loud, but not by pressing harder. Remember, you don't want the paper to pull out of the bulldog clip. Go slow and steady. Newsprint is actually pretty good stropping media, and fine to use while you choose, order, and wait for your real strop.