Going to go ahead and address some of this for you.
1. Not true, using an alarm bell causes all non military gnomes to flee to the great hall, any military gnome not assigned to active duty will be able to flip levers and reset traps if set as a mechanic.
2. I won't argue with the fact that traps being considered the same job as other mechanical orders causes issues. This could be addressed by build/play style or a change to priority and job type.
3. They will attempt to reset them only if they have a path available to said trap, a mechanic job is picked up first by proximity so interrupting a mechanics path to a trap can cause them to pick up a closer job (IE that lever by the gate they got stopped at)
Traps have been in a "love/hate" state with this community for a while. I personally rarely ever use them, and the best results I have seen with people who use them is as an early warning/softening tactic for strong military kingdoms.
I view traps as a waste of both gnome power and kingdom value/space considering the value of material needed to perform well at a job they only do "once" a fight.
My personal favorite of the suggestions that pop up about these issues is implementing a "forbidden" tag for items, traps, and locations. (IE any trap that gets set off is "forbidden" until you assign a reset job, or any corpse not killed by gnomes is forbidden until selected)
Bonus tips. Don't auto butcher corpses, and only unsuspend a corpse stockpile when needed. (Just a quality of life thing if not using mechanics to protect suicidal gnomes)
I often have an automaton that sits in a box and makes coal day and night until a mechanic order pops up, he is assigned to the military but does not fight.
Here is a album showing how to have an alarm bell set to automatically be rung the moment something comes to visit. http://imgur.com/a/p3UQs
This can be expanded upon to fit many situations, just keep in mind to set the job order first. (The job wont be attempted until a path is made available)
Edit: I would like to point out that I may have sounded overly negative of the regular traps, I would like to say that they do have a use and are a viable choice with vanilla settings.