Yes, that is plenty, otherwise they wouldn't have sold you that connection. You won't see your bags until you get to Munich, so that's also where you'll be going through customs, not Hamburg. You will go through immigration in Hamburg, but 90 minutes will be more than enough. I'm pretty sure you will arrive and depart from Terminal 2, but in any case both terminals are connected airside. HAM is a lot more compact than EWR.