Do I need to rebuild indexes after importing a .bacpac into a database? Do I need to rebuild indexes after importing a .bacpac into a database
or does the database takes care automatically?
There is no such magic in SQL Server!

Although, IMO it would be a great if Microsoft provide such options in the future. 

So, you have to do rebuilding indexes on your own. 

The good starting point is a set of scripts provided by Ola SQL Server Backup, Integrity Check, and Index and Statistics Maintenance.