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(Jamie Jackson)

I've got a lot of drilling to do in iron (?). This is the kind of
metal sold in the hardware store along with angle iron, etc. It rusts
fairly easily, is magnetic, etc. It's 1/2" wide and 1/8" thick or so.
I'm describing it because I don't know exactly what it is (iron or
steel).

Anyway, I've got to drill lots of ~3/16" holes through the stuff, as
well as countersinks for wood screws. Last time, this was really
slow-going and hard on the wrist (I've only got a power hand drill),
especially the countersinking (boring bit is Titanium Nitride,
countersink bit is high speed steel), and the countersink bit dulled
quickly. Should I be using a lubricant, and how do I approximate the
right speed with a hand drill?

As previously stated, you're drilling mild steel.
Yes use lube. (I like the soapy water suggestion)
If you have a combination drill/countersink bit, that might help. I would
suggest a machinist's center drill (combo short drill and 60 deg countersink).
Wood screw screw heads are not at that angle, however. They may be close
enough so you might try that anyway.
FM