Customfield Selection and correct value renderer?

Hey there,

I have a Velocity template which will be rendered as a project panel. I want to add an select element for only the project specific customfields. If the User select a customfield he sould select a valid value for the selected customfield.

My first thought was to get the customfields via REST but I can only get all Fields that configured in the whole JIRA-System. So how can I get a List of Fields which are only configured for the particular project and how can I get the right Renderer for that specific customfield?

I got now all Customfields that belong the specific project, I passed the projectId to the CustomFieldManager to get a Collection of CustomFields.

How can I get a Renderer for the specific CustomFieldTypes?