Fetch data from SQL Server table of the ERP DB
If you really want to move lots of data off the source server often, maybe you should consider the db's native solution of  


Replication.  


You can organize it to push only what you want it to push.
It is made to operate in parallel to normal operation.  There are lots of configurations to balance getting it thorough versus not bothering the server too much (at both ends).  It can do things like read transactions logs with separate Services, avoiding running queries through the db engine at all.  

There's a ton of information out there.
You can start with the official stuff at:
https://technet.microsoft.com/en-us/library/ms151198(v=sql.90).aspx
It walks you through a lot of the options, including
choosing an overall Replication type,
and considerations for Data Warehousing and Reporting scenarios.  

Any internet search for more help on Replication, including on SO, will turn up a lot more.