Storing luggage

You can normally drop your luggage at the hotel before check-in and they will store it for you until your room is ready. I should say you are checking in early even though your room cannot be occupied until late afternoon.

I usually do what Sam recommended— store luggage at the reserved hotel when arriving before check-in time. Hotels usually can not promise early check-in in advance because they don’t know what time the previous guests staying in the room you will be assigned will be vacating. They also don’t know how long it will take to clean the room until housekeeping actually opens the door and sees what is required. Some people leave rooms quite clean while others leave a mess behind.
Munich’s main train station— Munich Hbf— does have lockers for rent which is ideal if your hotel is a distance away from Munich Hbf.

Here's another vote for storing luggage at your hotel. I do not know of any hotel that would refuse to keep a guest's bags for them until they can check in. It's definitely worth an ask.

Hotels will always let you drop off your luggage while you go out sightseeing. They will keep if for you after check out too.