Hi Ron,
I'd say there is no such thing as the "correct" gauge when it come to resistance wire. It's a matter of the application, what you want to accomplish, and what works for you.
I've rebuilt quite a few protank coils, and have settled on 30 gauge wrapped on a .097 arbor. I tried as large as 28 gauge, but was tearing up grommets during assembly, and the thermal conduction was burning the grommets too.
Note that a .097 arbor won't fit into the slots of most protank heads. to get around this, I wrap on a .097 arbor, then have another .097 arbor that I've flattened two sides of. I use this to support the coil during assembly.
As to the number of wraps, I use the steam engine website to tune that to the target resistance, anything from 1.4 to 2.0 ohms.
Oh, and just my opinion, but I think it would be very difficult to use 24 gauge wire in a protank coil. not much room, thermal conduction to the grommet, getting it assembled, etc. I think it would almost have to be sub-ohm, and the protank really just ain't meant for that.
Wayne