Thanks for your feedback. I'm a step further now:
– I can search on users. However after clicking on a found user, you will be forwarded to the post that the user has made. But is it possible to redirect the user to the profile page from the users? For example: when you search on: “Eef” it would be great that the user will be forwarded to the (dynamic user based) url http://acceptancetoggdib.nl/muziekprofiel/eef/.
– The setup for custom fields works perfect, really nice! But can you tell me how I can change the background from the created pulldown menu's? Must I change the css code manually for this, or is this theme based?