Hi,
I think it was pretty good, nice job!
It is not too long at all.
You could probably talk more about “number” column and the ability of DataGraph to do column-wise operations, which I think new users might find it helpful. But yet again this is a Getting Started Guide and I can see why probably you choose not to include it.
Another thing that might be missing and I personally find it very useful is the functionality of DataGraph that by hovering mouse pointer on a setting for couple of seconds, it briefly describes it.
Also, the question marks on objects might be a functionality of great use for new users. Both of these are self explanatory but it might be helpful to have them in this guide.
Good luck,
Kourosh