Se pueden poner bastantes mas palabras claves hasta 500 caracteres,ademas se puede poner una descripcion con las palabras claves entre otras cosas,y en el titulo del video tienes que poner la palabra clave tambien.
I use to go after multiple subjects with similar keywords. However, the longer term play is to make three different videos and create a playlist with those three very good keyword phrases. That way you have more content, and can link back to the playlist getting more longer term success! I usually focus on one main keyword, and if I think I can, try to shape a playlist around it!