I will answer even though I'm not a guy.
The docs for SQL DB will answer your questions 1 and 3.
SQL DB doesn't have versions like that. It's a service, so you would migrate to whatever the current version a the time you provision the database.
You can use Data Migration Assistant https://docs.microsoft.com/en-us/sql/dma/dma-assesssqlonprem?view=sql-server-ver15 to help your evaluate feature compatibility between your on-prem SQL Server and the Azure SQL DB service. I'm not sure there's always a case for using it for migration ("it depends") but the compatibility analysis it does helpful.