I couldn't tell you much about the value of steem, but where it concerns content producing a good rule of thumb is to go with what can be consistent. If that's video start there and gradually increase the frequency of text articles if that's what you want.

As for the platform, the fact that it is the internet means that the consequences are quite reduced. It's probable that not making it big on any of the platforms will have little to no drastic consequence on your life. Thus I'd say try them all and see which is or are best.

All the best.