Hello - just watched the video on honing. Besides making sure the steel is magnetized, what else should I look for when selecting a steel? Also, how many "strokes" are enough to get a knife honed? Or do I just try cutting with it and see whether it's sharp enough?

Look for weight. The heavier and thicker, the better. Always start with just a few strokes, about 5 on each side and then test it. If it needs more, then do more. But if more does not help, this is a sign that your knife needs to be sharpened on a stone and beyond the help of a steel.

Why advantage does a magnetized steel offer? I have an unmagnetized steel already that I have had for years and it works well.

The magnetic properties of a metal steel help catch the shavings, but also help align/center the micro-edges. If your steel works for you, keep using it. But generally, magnetized steels are also a sign of better quality. The key is its weight and thickness - the heftier, more dense and finer the steel the better.