Double wall wheel rim - These can be nice, but there were some nice ones in the past that were not double walled such as the Winnemann Concave. Recently I have been using the Velocity Dyad which are double walled.
Double butted spokes - I think unbutted 14 gauge spokes work well for touring, I don't think you need double butted.
At least 36 spokes with three-cross lacing - Yes, and maybe more spokes if you are a big guy or take too much stuff.
Brass nipples - Yes, I would not use Aluminum nipples on a touring bike. Al nipples save weight and build up nicely but will corrode over a year or two making it difficult to true the wheel later on. Save these for your racing bike.
Double eyelets - These are less common than they once were. I don't worry about it too much.
What is important and this is why your sources say to get a handbuilt wheel is getting the tension correct on the spokes. Rims have a maximum tension recommendation. If the tension is too low the wheel won't have integrity and will give you problems. If it is above the maximum tension the wheel will tend to break itself apart over time in the form of cracked rims or eyelets popping out. If the tension is correct the wheel lasts a long time. Building by hand with a skilled builder is a better wheel than a robotic machine made wheel which is probably how wheels are made from some mail order house advertising touring wheels for $125 or some such thing.