Hi Mike,
In ECC side
1. Set the master data for your planning, ex Finished Products, Components, Plant , Work center, Customer, Dist Centre, Capacities, ATP categories, Consumption Scheduling and Planning Strategies followed by BOM, Routing, Prod Version etc.
2. Create the sales order.
Cif the Master Data first then your transactional Data viz your SO, Stock, Planned receipts etc.
Now you've your data setup ready for planning SCM.
Set the planning parameters and profiles for your SNP planning engines in APO (Heuristics, CTM, OPT)
In MTO there wont be any planning done on Future demand so your production will only start after your Order gets created (SO).
you can run SNP Heuristics (infinite planning without capacity constraints), CTM (Finite Planning without Cost Constraints ) and , Optimizer (Finite Planning with Cost and Capacity Constraints - These planning engine serves the same as MRP + CRP in ECC,
The result would be requirement planning proposals (in house production/ext Procurement of finished / Components) based on your available stock + capacity planning proposals on your available Capacities in work centres based on your available capacities.
Proposals may be Planned order or Purchase Requisitions which tells the system what to be produced/procured from where in what qty on what date and the same will be CIFed back to ECC or sent to PPDS.
These orders can be converted into Production Orders or Purchase Orders either in ECC or in PPDS if you gonna use PPDS in APO and then the Firm orders will be sent to ECC from PPDS.
Finally Production execution will happen in ECC based on your Sales Order.
I tried to give just an overview.
Regards
Vinoth