I don't know, I didn't bring a suitcase, however nobody there that day walking into the grounds or standing at the entrance line had anything. Backpacks stayed on people, I didn't see any disappear. So I think not.

I can’t answer your question directly but it’s easy enough to pay directly on the day of your visit at the palace. Hope this helps.

Il castello di Nymphenburg si può dire che è in città. Si raggiunge facilmente con la metro e poi c'è subito la fermata di un bus (non mi ricordo il numero) . Va bene il biglietto che si usa per girare la città. Se invece la meta è Dachau deve prendere il biglietto per la zona maggiore.

Sorry, I am also unfamiliar with winter events in Munich.

If you intend to spend some time there it is best value to buy the Combo.

I don’t know about a taxi, but what I can tell you is that if you take the 16 or 17 tram to Romanplatz (as there are some construction works) and then take the 17 replacement bus (all of this is very cheap as you buy one ticket for 1 zone) then you arrive directly outside the palace. This is how I travelled to my hostel and saw the palace on my trip, and decided to go. This does not take long at all to do and is very easy to sort out- I think this would be much cheaper than a taxi, and would take around the same amount of time.