Replica of SP online Production Site for Development Purpose

Question

Hi,

 

Requirement:

 

Creating a replica of production sharepoint online site collection which would serve as a development site to work on before making changes on the production sharepoint online site.

 

 Questions:

 

1) Would it be better to go with a fresh tenant or stick with the existing tenant as it would be just a site collection for developers to work on? How do other companies setup their sharepoint online development site.

 

2) Can i use the Sharegate Tool(Trial version) for copying the data from the production site to the newly created development site collection.

 

3)How much time would it take for me to copy the structure and contents of the source site to the new site(Size approx 4-5gb)

 

4)Will the masterpage for the source site be copied to the new site if a custom masterpage is being used on the Production SP Online site? 

 

5)If I currently have 15 subsites under the main site collection, how should i proceed with the migration using the Sharegate trial tool? 

 

6) Am i right when i say "When creating a development sharepoint online site  all i need is the structure and the look of the source site. I need not have the content migrated as the data on the production site would be confidential".

 

Please advice..