How to insert a large amount of records to the database in a short time?
There are several options.  Here are the main ones that come to mind.

SSIS - SQL Server Integration Services: This is SQL Servers ETL tool and you can move data from pretty much any source to pretty much any destination and it can be quite fast.

BCP - Bulk Copy Program: This is a command line tool that comes with SQL Server.  It's very good at moving text files into SQL Server or you can export into a native format from one SQL Server and import using that same format into another SQL Server.  BCP is also very fast but a bit more limited than SSIS.

INSERT INTO tablename SELECT fieldlist FROM othertable: This assumes that you are moving from one SQL table to another on the same server.  This is the fastest but at 500k rows you are looking at a fairly big transaction or having to break it up like you said.

OPENROWSET: This is a SQL Server function that will let you pull data into a table from various formats.  It's also supposed to be fairly quick but I haven't worked with it much.

General note: Your primary key is mbr_id.  If this is something that is stored in your source data (as opposed to being an identity column) your insert will go MUCH faster if the source data is in mbr_id order.