All very good ideas for Ken's comeback.
I think what's needed is someone who's a "cheerleader" for Ken. Someone that can point him in the right direction. The reason for this "cheerleader" is, unlike singers like Rowena, there's a certain group of people, from the HK entertainment "reporters" to loud mouths like Lam Mun-chung, waiting to make trouble for Ken. I don't know what are their motives, but whatever they do will harm the progress for Ken.
I like to see Ken do his concerts, but I think a few guest performances will also be good. I'd like to see Ken guest perform at Andy Lau's upcoming concerts, for example. A well-received performance for a couple of songs at such a concert will build up Ken's confidence. I also hope some of Ken's friends in the music business can help him out.