The problem with the installer freeze at 12% seems to be solved at the 9.0.1 iso. When i did a fresh install (without additional firmware) with the "debian-live-9.0.1-amd64-xfce.iso" on the Acer Aspire E11 (ES1-111-C5Q9) the process ended up with a fully working debian installation.
I previously also tried the "firmware-9.0.0-amd64-netinst.iso" on this laptop but then the installer hangs again at 12% ( installed discover) .