This sounds cool.
I think most of it depends on what options the control has. When you add it as a custom control there should be a list of parameters that can be set. Have you looked at these to see if they might control some of what you want.
I am pretty sure number 3 is fine. In a published form the user cannot change the size of a control. I am not familiar with this control and it does not seam to show up in my list with 2007 but if there was a way to use a sheet as a template that would accomplish what you were looking for.
Another option, probably not as pretty would be to use a file attachment control and allow them to attach a excel template to it.