• We have updated our Community Code of Conduct. Please read through the new rules for the forum that are an integral part of Paradox Interactive’s User Agreement.
I think "low grade" sources produce more waste rock? Not sure. Anyone know for sure?
 
As Brazil, I highly recommend going with the Rocket Scientist commander profile - that way, you can easily set up concrete mining operations in remote places. You'll get lots of waste rock, and you can trade away some of the thousands of units of concrete you get to your rival colonies for metals, food and polymer quite early. Buying probes to scan for concrete faster is good, especially if you get the Advanced Probes research early.

Water pumps for waste rock are a bit more risky in terms of colony longevity; you'll need that water eventually, and storing it in water tanks isn't optimal given how disasters can cause leaks. You can buy concrete if you somehow run out. Not so much water, barring moisture vaporators. :p

While some other commander profiles increases the raw output, the shuttles allow you to get the waste rock (and thus rare metal) earlier, which is usually better.
 
In my experience about 4-5 extractors should provide enough waste rock for a single refinery.
Early on you can get some waste rocks from boulders by placing landing pads and canceling them once the drones clear the area.