Tuning a Proform/Holley carb, what parts and tools?

It's hard to state definatively what is correct with many of these new carbs because the transfer slots are often longer and/or wider than the old school Holleys. About .020 to .040" or square looking should still be ballpark, but go with what works.
Longer and wider, all other things being equal, means that at idle more air bleeds in the top and as the throttle opens the ratio of air bleeding in the top to fuel out the bottom changes to richer quicker than a narrower shorter slot.

When you feel like doing some reading:
Transfer Slot Length? where the length is directly reduced using a set screw in base plate.

More commonly if the slots are too wide or long (ie causing tuning problems) a restrictor is placed in the transfer slot feed. This helps lean out the low throttle above idle. Nailing the exact size is a matter of testing. The fuel at this point already has air bled into it so it can be very sensitive.
A couple of examples:
Carb Help
Holley 870 Avenger Converted to 4 Corner Idle
Just so you know that success will eventually be attained. :)
Proform 850 Race Carb Update!!