Volumio with Waveshare 4inch HDMI LCD

today I tried to add the Waveshare 4" LCD to my setup (Rapsi3 +IQaudIO PI DAC+).
Wikipage for LCD: http://www.waveshare.com/wiki/4inch_HDMI_LCD

After I have appended the following lines

hdmi_group=2 hdmi_mode=87 hdmi_cvt 480 800 60 6 0 0 0 dtoverlay=ads7846,cs=1,penirq=25,penirq_pull=2,speed=50000,keep_vref_on=0,swapxy=0,pmax=255,xohms=150,xmin=200,xmax=3900,ymin=200,ymax=3900 display_rotate=3
to the config.txt and installed the touchscreen plugin it works rudimentary. I’m stuck at the moment and have some questions. Hope somebody can help me:

  1. I’m using the Quad Dac+ so most of the Raspberry pins are already used. So I connected the LCD just over HDMI. Is there still a possibility to enable touch functionality?

  2. It seems like the display only works for a few minutes. After that the screen goes black. Is this maybe some kind of power saving, since there are no touch intputs over the display? Once it is black, it’s hard to reactivate it. (I was once successfully, but can’t get it to work again)

Any advice?