No harm to the amp. The amp will go through it's normal turn on cycle.
There are lots of better amps as well as lots of worse amps out there for $800. I don't have the slightest clue because I don't know what you plan to hook them up to. Does the $800 include the preamp and tuner?
If memory serves, the On/Off button is mechanical so if you plug it into a switched outlet that can handle the amperage and as long as you have left the power switch in the on position you should be good to go.