Hey,
can you give us some information about the date? Because it is difficult to help you without
Ofcourse! I was planning to go around 11th of July. :)
Please don’t use the rail planner app to plan. It doesn't get enough updates to be reliable. You could be in for nasty surprises.
The night train Munich - Florence - Rome does not run in June and July because of engineering works. You could take the night train to Venice and change to Florence, although that will take another travel day.
In addition, 11 July is after 12 June, which is the start of the summer timetable. Trenitalia still hasn't published that timetable. The Nightjet München Ost - Venice can already be booked though (best via tickets.oebb.at using these steps).
Due Construction works there will be a short time this summer in that the NJ Vienna/Munich - Milan/Rome wont operate.
The Nightjet Munich/Vienna - Venice will be rerouted via Slovenia.
As said Trenitalia havent published their final timetable for the summer (they do it usually atleast in April)