Pierre,
Try to be clear about what you want to do, You my need only one module in Eloqua or you might use them all.
Try to map out your process and figure out all the questions you want answered and things will become clearer from there.
Do not try to overload one process or program instead build small processes/programs you can optimize later when each pieces are working.
We are an event business, we do not use Eloqua or system integrated with Eloqua for registration but we are still able to to run our post registration nurturing effectively. The process includes regular update emails, Up-sell campaigns and even SMS.
It is all possible one you have a clear picture.
Good Luck