Thank you for your help, I think this solved my problem. I thought about your proposal and agree that it would make sense to integrate this information via the likelihood instead of defining a Gamma hurdle prior for the intercept. I think I was trying to incorporate my expectation on the rate of 0’s (i.e., 5%) directly into the model, but doing this by a gamma hurdle prior for the intercept would be incorrect. I still think that this expectation should be somehow reflected in the prior for the model parameters, but my results obtained with a noninformative prior seem still valid and plausible.
