Teemo should get wards for river. Mushrooms may not be enough to stop a gank. Use the mushrooms more in jungle or lane, rather than terrible river vision. (Unless you're really really trying to set up a massacre zone around Baron) --- http://i.imgur.com/ZhLrT.jpg http://i.imgur.com/H6Frl.jpg
Depends. Early game I'll grab a ward, and depending on what side I'm on I'll use it early or not (to help jungler). Also will depend on if I am ganked or not. If flash is down, ward up.
Then at level 6, you can make a full wall in the river with just 3 shrooms. At that point, just ignore warding tell it becomes relevant to your team, because the moment someone hits one of those shrooms you can just book it out of there. --- Cyber Troopers Virtual-On World Champion