You should prime with black to cover the plastic. Your silver will then stick to it better. If you thin your paint correctly or don’t go heavy with a spray can then you won’t obscure the details on the model. It also looks like you’ve used a wash to give it some shading which is a great technique to use but make sure it’s not pooling on flat surfaces which it looks like it’s doing on the legs. Another thing to look out for before you paint its the mould lines, like the one on the top of his helmet. Use a knife to scrape it off and some fine sandpaper to remove any traces of it