Is it safe to add more than primary data file to Temp DB in SQL server 2008 R2 as we have database server with 4 Core processor?
The article linked by @McNets is a good one. 
The One And Only One article has code you can use: https://www.brentozar.com/blitz/tempdb-data-files/

Because you only have 4 cores, you can probably just create a total of 4 TempDB files. 

If you use the code snippet in Brent's article, make sure you match up the beginning of the file name section:

FILENAME = N'


with the folder directories you already have. 

You don't have to restart the engine if you're not shrinking the the original file while adding these. As for the size, it's not necesaarily a bad thing that it is bigger than your prod database, though it could be indiciative of something. Do you delete a bunch of records out fo there recently?