ok about the Transient structural settings. However, my contacts involve bodies which could come in contact during motion since at initial configuration there are clearences between all the bodies. So I'm setting frictionless with pinball radius a little bit larger than the gap to make them near open as you suggested me. Is it ok?
the following picture explains better the contacts I plan to set by identifying them using different colours (only upper block is shown since the lower one has the same contacts)