Sometimes I am playing a game while watching some streaming, and then fall asleep in the middle of it. Any pending downloads won't start until I manually resume it. I already have some applications like this, but I automatically turn off my PC when I fall asleep to prevent wasting any electricity. Is there some way to make downloads automatically resume after being away for a certain amount of time?
If you have the mobile app, it allows you to remote control the download of games to your devices.
Steam would have to be currently running on the remote machine though.
If you have manually paused it then you have resume it manually.Also You can limit you bandwidth to lowest (25kbps I guess) so it won't affect the speed and quality of streaming videos. Or any other speed is preferable to you. Go in Steam Settings>Downloads>Limit your speed etc. Good luck
You can allow Steam to background download games on a per-game basis via the properties menu of each game.
If you disable this on all games via Steam settings, then the downloads should resume as soon as you quit a game.
Here's a question that has a lot more details about these settings: How do I continue downloading a game in Steam while playing?