Well this is my first post from the Nexus 5 and I must say I'm really impressed!
As I'm getting lots of app installation notifications, is there an easy way to dismiss them all at once?
When you pull down the notification shade there are 3 staggered lines, click that and it will dismiss all non permanent notifications.
Go into language settings and disable(uncheck) all of the other keyboards but the one you wish to use. go to applications settings, find the "all" tab, find the other stock keyboards and disable them. restart. worked for me.