Topic: Hardware Power-on time length of Fireface 400

Considering Hardware life-time , how long Can I keep my FF499 turned-on ?
My PC is always running , I never turn it off  in months , I have An Internal audio Interface too , should I use it  (internal Card) for common usage ? or I can  keep The FF400  turned on all the time ?
if I keep both  Internal (on-Board) and FF400 Cards enabled at the same time , could it be a RME Killer ?
for turning-off the FF400 is it safe to just Unplug it ? or it can be only unplugged when the PC is Turned off?
Thanks for your support