This is uncharted territory for me. Done similar stuff with wood using Brad
point and Forstner bits but never with metal. Basically, I need a
counterbore (CB) diameter of about 3/4" to a depth of about 3/8" in 1" thick
6061 aluminum. This is to create a recess for cap screw head and washer
along with room to use a hex socket on the cap screw.

Sourcing the correct CB and pilot seems easy enough except that MMC
recommends HSS ($$) for ferrous and carbide tipped ($$$$) CB for non-ferrous
metals. Surely, HSS should work for aluminum or am I missing something?
Also, what would be the best drill speed to use in a case like this? I
normally use wax lubricant for countersinking metal, is this good enough for
counterboring? Finally, is it advisable to buy say a 1/2" aluminum blank and
practice first or am I making a mountain out of a mole hill?