With that size, flat files might be a better option as you won't be using both databases while transferring the data through the network.

Script just the structure, not the data. Then use SSIS or anything similar to move the data from one database to the other.
You can't downgrade a database. For that...

SSIS is better handling errors as you can send the problematic rows to a different destination.
T-SQL can be faster and easier to write. But, as mentioned by Alan, it...

I don't see why wouldn't you.

CREATE TABLE SomeTable(
  SomeID int PRIMARY KEY,
  SomeValue varchar(100),
  SomeDate datetime
);
INSERT INTO SomeTable
VALUES( 1, 'A',...

Maybe something like this would work.

SELECT COL1, COL2, NEW_COLUMN
FROM TABLE
CROSS APPLY (VALUES('COL3', CAST( COL3 AS varchar(100))),
       ('COL4', CAST( COL4 AS varchar(100))),
       ('COL5',...