2. Yeah toxic players really can ruin your enthusiasm for the game. As soon as someone starts becoming toxic, just instantly mute them, don't wait for them to start flaming even more. Once they start they never stop so just mute them for your own benefit.
3. I think that's common for a lot of people. It's easy to say from an outsider perspective but always prioritize your mental health. Consider if you think reading a book for an hour would be more beneficial to you. If so, then why are you playing Dota?
I would say just try to play some unranked games and see if you enjoy them more than ranked. Enjoying the game is more important than getting rating. Even better, try to play some unranked games with some guys from this site.
Don't waste your life away on something that gives you that much anxiety. I had the same thing with Starcraft. Sometimes you just have to accept that a game is not good for you mentally and it can be better to just be a spectator. We already get enough stress from work/school as it is. So there is no point using our valuable free time to do something increases that stress and anxiety.