I'd vote for using a Weber daisy wheel. It's obviously works well, as a lot of people use the Weber lids on their drums. You have the ability to seal it up at the end of a cook, won't need to buy a hole saw. You may still need a bit (not sure of your tool situation)...but if you get a step bit for the intakes, you could get one that would work for exhaust as well. I think the Weber holes around roughly 3/4"...not sure what your plan is for the intakes, but you could keep it simple and go 3/4" both in and out.
Just my $.02!
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