I'm new on Qlik Sense and I'm wondering if it is possible to create a template with all the data operations declared and then each month use this template to create a new app passing the month data and avoiding to do all the creation of visualizations again.
Yes it is. It is fundamental to all BI systems to allow creation of applications that will not need to be adjusted when new data come in monthly or on any regular update.
You will have to make sure that your data gets transformed so that you don't have crosstables that have columns that have some time element as the column name.
This can be done in Qlik Sense by for instance using the CROSSTABLE LOAD to unpivot the time dependent column/field names into a more flexible table structure that makes it easy to create visualisations that can adjust automatically for each update.