Hi Deven,
Part 1 :
If I understand your requirement correctly. You want the STO to be released automatically or should be approved when they are created and not follow the normal approval process for purchase orders.
What you can do is create a custom PO type for inter company PO. You can then use the PO Type as the characteristics for release strategy and exclude the Inter company PO type from release strategy in CL24N.
When you do this all the other PO types will have a release procedure but inter-company PO would be available as soon as they are created by the system.
Part 2:
For the second part you need to look into config for availability check for the inter company STO.
The node for the same is :
Sales and Distribution -> Availability Check and Transfer of Requirements -> Availability Check -> Carry Out Control For Availability Check
You can choose different kinds of stocks you want to consider from here.
Regards,
Amit