Hi @rob.stallman,
Thanks for your question!
For your first point, you are absolutely correct.
For your second point, the PSETDEF values are taken directly from the IEEE 39 bus system. We recently received a very similar question about demand, and I’d recommend you check out the response to that here.
You could certainly correlate the total demand in this system to historical ISO-NE demand. If you were to do so, you would need to add additional generators to serve the additional demand and you’d likely also want to keep in mind the PMAXDEF values for each line to ensure enough transmission to meet that demand.
Happy modeling!