I'm not sure you get the 100 free auction on both sites (perhaps someone else who has tried it can confirm), but the rest is correct.
You also of course get to benefit from any listing promos that you qualify for, so potentially your monthly free listings could be higher still.
I usually maintain around 120 - 140 listings per month and "top up" beyond that using the promos. I honestly can't recall the last time I was actually billed for a regular listing fee.
This works extremely well as long as you can predict fairly reliably how many listings you'll need per month.