Regarding your question how to engage yourself, you may travel from University to University and preach as you suggest, or you may go and work. For local work or engagement you consult with Hamsaduta and Tamala as they are in charge of the Hamburg management. After all we have to fix up our Hamburg Temple still more.
Regarding your staying back during Rathayatra, I think that is just a nice arrangement because someone must remain with the Temple during the absence of the others. Also since you are having some trouble with the immigration because of draft, and you already got a nice German wife, the best thing will be to make your headquarters there in Germany. So in this way manage things nicely in consultation with Hamsaduta, and Krsna will provide you with ample opportunities according to your sincerity to spread His Movement. Just try to make our Krsna Consciousness Movement strong in Germany and you will also automatically become strong in such devotional service or Krsna Consciousness.