I either need a Toaster to notify users of changes or even errors that automatically go away after a set time out. Will there be something like this in Blazor controls? If not do you have a general MessageBox modal dialog?
You make one with the AnimationContainer at this very moment: https://demos.telerik.com/blazor-ui/animationcontainer/notification.
In fact, you can also use a Window component, as it is another popup (you just have to toggle its Visible parameter, like shown here: https://feedback.telerik.com/blazor/1408055-busy-indicator-which-is-mvvm-friendly).
You may also want to Vote for and Follow the implementation of a richer component for notifications: https://feedback.telerik.com/blazor/1425097-notification-controls.