1. Can't wake up your PC with controller. Workarounds with custom scripts and WoL are ridiculous. They also don't solve having to log in afterwards and starting a game.
2. Because of missing HDMI-CEC, you have to switch to PC output manually on TV
3. Same issue in opposite side. PC stupidly uses TV output even if TV is off. If you want to use the PC without TV, you gotta disable TV output. What's that, you can't see display menu so you can do this? Yeah because that menu showed up on your TV that is off, since it's set as primary display, which is needed for games to launch on that screen.
For first issue, you gotta walk to your PC to turn it on, login and launch game. For 2) and 3), it's easiest to plug in cable in TV when you need to and plug it out when you are done.
I don't know why there isn't a consumer product yet solving this without hassle.