I'm going to agree with this approach keep in mind that your system is going to need to be capable of processing 10 transactions per second in order to keep the dataload under 24 hours. If we were using Middleware/XIF a decent system can process three to four BDOC's per second. The problem is if you do parallel processing the bottleneck is going to be your database update performance so just because you can run parallel programs on the app server, doesn't mean your system will handle it at the DB level.
Hopefully you have some pretty big hardware, because an initial load at those datavolumes is going to take a while no matter how great you optimize it.
Take care,
Stephen