There is a huge difference between 10 hours multi and 100 hours multi. Actually, there is a big difference between 10 and 50. There is not nearly as huge a difference between 100 hours multi and 200 hours multi, however. Teaching multi engine is also extremely helpful, although it is better to do it after you get some multi experience.

As far as engine failures are concerned, I get a minimum of 3 engine failures every six months, like it or not. This occurs at recurrent training and checkride time, and at least one is under the hood on approach so that you can handle it in the unlikely event where it really happens to you.

Good luck, and don't underestimate the value of your light twin time. I would recommend flying something else though. Not because there is anything wrong with the Diamond, but to give you a better idea of what typical twin flying is like. A Seneca, Baron, Aztec, Navajo, Twin Commanche, Twin Otter and King Air are extremely different than your DA42.