Even though a CLR trigger can actually be an After or Instead Of trigger, it is still a unique type and makes the answer to the question 3 instead of...

After looking at BOL, it would seem you can specify SQL Server authentication for the OPENROWSET command. For example:

OPENROWSET

(

'SQLOLEDB.1',

'Provider=SQLOLEDB.1;Integrated Security=SSPI;Persist Security Info=False;Initial Catalog=AdventureWorksDW;Data Source=localhost',

'SELECT TOP 1000...