Those liquid stains from StewMac look suspiciously like TransTint (they tend to rebrand stuff they find and jack up the price); here are a few tutorials using TransTint I made last year:
[youtube]https://youtu.be/pwpFqWOVlH4[/youtube]
[youtube]https://youtu.be/KGsX2Pzjhfw[/youtube]
[youtube]https://youtu.be/jjQlJQ4AgC4[/youtube]
The trick is to find the right dilution ratio which varies by brand and color.
First you'll need curly maple to practice.
Ideally you would order the neck without Warmoth's penetrating sealer, otherwise it may be hard to dye it properly.
With curly maple there is no particular trick to get an even finish I can think of.
Maybe you're thinking of plain maple that gets all blotchy ? Not a concern with curly maple assuming you have a very figured neck.
You may just want to open up the grain by wetting the surface lightly with water in order to get good dye penetration with the first layer of stain.
I generally use 180 or 220 grit for bodies and necks and TransTint, Keda, or Fiebing's dyes diluted in denatured alcohol (or isopropyl alcohol for smaller parts): sand, open up grain with water, let dry, dye, sand back, dye.
This body was done last week-end and I'm hoping to do the neck in the coming days:
https://www.unofficialwarmoth.com/index.php?topic=32743.15