Well it work a bit to dissolve calcium buildups, but it is not strong enough to remove al the calcium buildups in your coffee machine. Next to that, vinegar will leave a taste/smell of vinegar behind, which will influence the taste of your coffee. So always use a proper descaler such as Brooks descaler

Well the best thing is too much then too little. In some cases it is also advised to remove the steam tube tip from the steam tube, so you can access it from behind. This is advised if you rarely clean your coffee machine.

Well you do need to do this every ¾ months. Even when you have a water filter installed, this can only be done with machines which are fitted with a external water tank. Not the ones which are connected to the main water line.