Hi Selva,
There is no difference to plan the reorder materials in ECC or APO. Most critical part is data synchronization between ECC and APO. If you can do the planning for that materials in ECC why you want to plan it in APO? Also CIF and performance point of view better to plan them in ECC.
Anyway it's a business call, How you want to plan it?
If you are planning all your materials in APO then there is no need to activated MRP for plant in OMDU. Apart from that materials which will plan in APO will have MRP type as X0 so it will not plan ECC MRP. As in OMDQ for MRP type X0 Planning method = 1 Planned by external system.
Yes we need to have all other setting in place as I suggested in my previous posting.
In APO we use /SAPAPO/RRP3 product view and ECC we use MD04 so to access the MD04 you need to have plant parameter maintain.
Please refer the below given OSS notes which will help you out.
619973 - R/3 - APO integration and Customizing changes (document)
143314 - APO - R/3 Integration in Production Planning
Regards,
R.Brahmankar