Mauricio, thanks for the answer. By the way your blog was also very helpful %)
Everything's clear about interactions.
Try to avoid using script nodes.
Is it ok to use Script Nodes to make thing like "user = String.valueOf(userBean.Name) + "-" + String.valueOf(userBean.Id);"?
Regarding the operations with the DB which seems to be transactional, it depends on how do you want to do it. If you start a transaction against your DB inside a workItemHandler and then write the logic to see if everything else went right and commit that transaction, everythhing should work.
Could you clarify some things about DB: I found "Data Object" elements in eclipse designer palette, is it something concerning data access? Or what are they made for? It confuses me a little.
Notice that for what you describe, you don't need to persist your "Flows" because all what you need is to execute the steps and commit or rollback the information to another external database.
Also, concerning persistence and clustering: if I persist my flow instance, does it provide the ability to restart flow from the point it was persisted after system crash/shutdown and restoration to operational state? Could it be configured (coded?) to failover process instances to other running system restoring states from persistent store?