lisalisa

hi all; first time visiting and first time posting. if this has been posted elsewhere please direct me to that thread.
we are going to oktoberfest then on to italy in early october. i plan to make our vist train reservation online (munich to venice) but was wondering generally how the trains are set up. where do you store your luggage? can you lock it? we'd like to take a sleeper, maybe the 6-person couchette.
any advice would be appreciated!