Hi Pierre,
I would recommend following grouping.
1) Process1 -- As you mentiond (product, location, customer etc).
2) Process2 - group those tasks which do not have interdependancy, e.g. donot group productlocation & productcustomer, as you have product column common in between them.
3) Process3 - Individual tasks.
4) KF tasks - Dont group any KF tasks, it will go in error.
I think there is some issue with locking of table in IBP, hence you were unable to load productcustomer & productlocation as part of single process.
I would recommend you to do following test, run productcustomer individually and very next second run productlocation task. Once tasks are in IBP, monitor it, that do they get over or not?
It will take more time stored procedure will be running for both the task at same time in IBP.
Let me know results for this as well.
Regarding other strategy of 10mins difference, is a good idea, but you should take 5 - 7 runs of each task and then you will come to know avg time per task. Keep buffer of 5-10mins over and above avg time. This way process / tasks will run in sequence but will not overlap (probability is less).
Thanks,
Purav