Hi Dex
I am listing some of the challenges which you might face ..:there could be more as well
- Refresh of the system is also challenging you need to take backup of all the system at the sametime.
-Data visibility also important. User should not be able to see the documents belonging to other backend system. Roles should not have any open value like * in the purchase organisation or purchasing group.
- While replicating vendors from ECC to SRM, you have the option to retain the same vendor number in SRM. In this case Business partner number is same as Vendor number. Check out the input options in txn BBPGETVD.
-If you have different number for the same vendor in SRM and ECC, go into VENMAP.
For the ECC Vendor number, get the PARTNER_GUID. Go into table BUT000. Enter the PARTNER_GUID . you will get the Business partner number for this Vendor
-Even if they have same BP number, they will never share same GUID value so should be fine .
https://scn.sap.com/thread/1631345
1473217 - Connecting to Multiple Backends from SRM portal
I hope this helps
Regards
Vinita