The higher the helix the more voodoo involved especially on small diameters.
You've got three different views of a gear profile. I am not too involved with involutes but deal with straight flank thread profiles.
The axial view is taking a threaded rod and slicing it down the middle length wise, and looking at the flat portion.
The transverse axial view is looking down the rod from the end.
The normal view would be tilting the threaded rod to the helix angle and looking at the thread.
I guess before I get carried away to answer your original question, the helix is a function of how much travel to how much turn of the gear. your need.
I use tan^-1 (lead/(PI*pitch Dia.) to find my helix angle.
Think of it as a simple triangle.
The opposite side is your pitch the adjacent side is your pitch diameter (hence why involute gears can have varying leads because the minor diameter, pitch diameter, and outer diameter all have longer or shorter lengths) and the hypotenuse is your nut travel length. Also not to mention varying flank angles for constant engagement. The diagram below is opposite of what I mentioned.
Just remember pitch is lead/# starts so 1" lead on 1 starts is 1" pitch, 2 starts is .5 pitch.
Hope this helps and by all means I've never had to explain this to anyone so if anyone finds holes just reply back and I'll correct it.
I am still learning after 5 years of trial and error.