So, this project was on hold for the last three weeks as I had my apt bathroom re-done. I just resumed it and decided to give the hole saw a try. It worked nicely, I have to say. Here are some pictures for you.

As you can see 90% of the edges are nice, 10% a bit too sharp. However, I fitted the rubber finishing I planned to use, and it looks decent.

Server HDD temp, after 1 hr running with the new panel fitted, raised from 30°C to 33°C . It seems stable now.

Thanks again everyone for the many suggestions!

Edit: Sorry pictures 01, 05, 09 are too big to show in the post. Just click on them if you're curious, of course.