If you are playting with Propane Orifices, you need to know about
http://www.drillbitcity.com/ . They have super small carbide drills with fatter shanks so that they will fit in a normal drill chuck. They even have a "Propane Orifice" specialty set. You can also drill out a pre-made orifice to 1/4-28 and then it will accept MIG contact tips (although at .079 you are way past normal contact tip size).
Yo will to hook up dual tanks(or triple) before your regulator to keep the tanks from freezing. You will need dual flexible high pressure hoses with POL fittings on one end of each, as well as a T fitting.
Check out
http://www.tejassmokers.com/ and
http://www.cajunshoppe.com/pageidx.htm for propane burner stufff (regulators, hoses, adapters, pre-made venturis). I am making a home made BBQ grill setup and have been dealing with both companies quite a bit lately... both wasy to do business with.
If you put a needle valve in series with the orifice, you can compensate quite a bit for an oversized orifice and fine tune it. You can't really do that as well with just an adjustable regulator. Note that a needle valve does not eliminate the need for a regulator.
If the orifice gets too big, you may exceed the capacity of the regulator. If you can not get the rated max pressure out of a given regulator while gas is flowing, but you can if you put your finger over the orifice, you may need to use separate regulators on each propane tank. Adjust them so they each put out the same pressure independantly. You will definitly need a needle valve to adjust the gas flow if you do that, as adjusting the two regulators and keeping the pressures set the same will drive you nutso.