Yes, there are always things that will take "too much" time, but initially it's usually a good idea to think about what you'd really want. If you start thinking too early about performance you often end up with something that might(!) be fast, but isn't really what you want... So ideally you start to think about what you want, then identify where the performance problems might lie and try to fix that.

That's true. In any case, I'll explore the UI concept of on-canvas templates some more, and see where it leads.

Have a look at laidout (http://laidout.org/).

Of course! :)