The concept behind it would be to allow presence of entities in an area for a limited time.
I am planning to call it the aperture science human-usable microwave.

I will consist in an area defined by a cube of glass with intense red light (and maybe fog?) inside.
I'll probably create custom overlays to put them on the glass too.

Now on the behavior side :

It should make noise permanently (easy), and every X seconds, go off (making a louder noise, and its lights go even more intense) for two seconds, damaging the player enough to kill him almost instantly, and (here is the hard part) : destroy the cubes inside it in an explosion.

I read something about parenting an explosion to the cube. Sounds fine to me. But how can we make sure that the next cube generated by the cube dispenser will also explode?
Should I generate a new explosion? Then, how to tie it automaticly?
Should I cheat an teleport the cube in the cube dispenser?
Or should I just go the easy way, aka make plenty of explosions go off in the microwave when something was in it when triggered?

Any advice would be gladly appreciated, thanks!

In your prop_physics properties, you have the fields "Explosion Damage" and "Explosion Radius".

Set these to a non-zero value, and you can then make your cube explode by using the "break" input.

I'll try it. Thanks.