You must be a bit carefull here. For vectors/scalars etc. it is done in excecute because only there you are calculating the result data, hence only there you know which fields are available. As far as I can see your arrow types are fixed. Hence you can set them one time in your objects constructor.What I didn't get to work though is setting the strings in the "Glyph" dropdown menu. This should be handled by execute(). I tried to copy the way this is done for the Vectors, but nothing happens.... I've never used Qt before, so am probably missing something obvious here.
Also note that this code only sets the properties in the App part of the object, this has nothing to do with the GUI yet. in your task dialog code you need to set the property values to the dropdown menu manually. For example you can call updateEnumerationList like here to setup the list from the property.
In VTK you can chain as many fitlers as you like. You just need to make sure they are connected properly. The PCS Filter data structure supports this with the vector "algorithm storage". There you can store as many filters as you like. Than, you set the first one as source and the last one as target in the Filter. All other, that you connected between source and target, are simply stored in the filter vector. That should be enough to make it work.Right now, the filter breaks the pipeline. If you would add another filter behind it, that filter won't see any data.