Hey Tom, congrats on your migration to Cubase. As far as changing to different time signatures within a project, I think I can help.
Open a project, and press Ctrl T
This will open the tempo track. As you can probably guess by looking at it, you can use the pencil tool to draw in changes in the tempo within the timeline, but if you look at the upper left hand corner of the timeline window, you will see the current time signature (let’s say 4/4) in a little red box. Using the pen tool, you can click into the gray bar at any measure, and it will drop another 4/4 in a red box – Once it’s there, double click it to edit it. Simply type the time signature you want to switch it to.
Hope this helps.
Peace –