After using Ubuntu 17.10 on my mac (MacBookPro12,1) and removed all stuff created by Ubuntu to recover vanilla Gnome, I realized that Debian Testing will bring the same level of comfort without additional irrelevant stuff.
After Downloading & burning on a USB stick the Debian Testing image the installation starts correctly (Press alt key during mac boot to boot from USB stick).
The wifi network card is not installed by default as the proprietary drivers is not there.
After the reboot I connected to internet using my iphone over Bluetooth.
I configured the sources.list file like this:
deb http://deb.debian.org/debian testing main contrib non-free
deb-src http://deb.debian.org/debian testing main contrib non-free
deb http://deb.debian.org/debian testing-updates main contrib non-free
deb-src http://deb.debian.org/debian testing-updates main contrib non-free
deb http://security.debian.org/debian-security/ testing/updates main contrib non-free
deb-src http://security.debian.org/debian-security/ testing/updates main contrib non-free
The installation of the firmware-brcm80211 package from non-free repository & computer reboot I was able to connect to wifi.
My previous NAS (Qnap TVS-473) had too many issues since I bought it. I send it back to QNAP under warranty and have been reimbursed.
Looking for a similar model in the same range I chose a Synology DS918+. After one day, I must say it is a very good product. The all plastic box looks less solid than the QNAP but it is well finished.
The interface is good and configuration is really simple.
Even with the basic setup (4 GB RAM) and 4 seagate HDD (3 To) the NAS is performing quite well.