For the simplicity I'm thinking of getting a old case and cut out the panel and make it fit to the acrylic, so that will be enough? It will be perfectly safe?
Is it possible to make this lay down (instead of standing up as in normal towers) whit out any hardware are beeing damaged?
Yes and yes.
A PC case is literally just a metal box with removable sides, and mounting places for various things. The main thing you have to watch for is airflow.