I'm a bit late to the party, but I would personally use...
- correct size tap drill
- uncoated tap
- lubricating oil (not "cutting" oil)
A forming tap works much better with a bit of high-pressure lubricant (e.g. old-school 90-weight differential oil or something like STP). It's a forming process, not a cutting process.
Yeah, I like to use the correct size tap drill sometimes haha!
I never thought about using different lubricants for form tapping vs cut tapping! I just don't know how I would do that, short of swapping out the entire machine's coolant reservoir.
Why no coating on the tap? Is coating detrimental when forming brass??