Chromium can be gotten relatively easily: one of your options is to find chromite ore deposit or to get it as byproduct from other ores, then process it as usual; the other way is to get it from centrifuging sluice sand, I did this in my previous run, but I’d suggest you to do the legwork to find chromite as you’ll definitely need it in large amounts later on.
You can get some from it. It roughly yields 10 units of chromium per 100,000 liters of sluice juice. You can make 90 units of stainless steel with it.
Nope, it yields about 1 unit of chromium per 100,000 liters.