But my site is multiniche One article per niche so there are not a lot of possibility to use a lot of keywords..
Yes using the keywords you want to rank for as anchor text is going to help you rank for those phrases. It's impossible to give exact advice regarding %'s, because you can find examples of everything working in the serps. Looking at what %'s your competition used is a good starting point. You can use ahrefs for this.
You can rank keywords without having them in your article!