Triggering mechanism should use practically no energy (spring pressure plate, the weight of whatever on it triggers it, and when they move off, the spring reset it). Now, due to simplicity, the pressure plate controls a metal wire/rope that controls the trigger mechanism of the actual trap, which uses energy.
And a small pressure can trigger a massive trap (think hair-trigger for guns).
Another thing to note is that some traps (swinging blade, serrated circular saw, etc) can be powered similar to a clock mechanism with just counter weight and oscillating. Therefore they can store a certain amount of energy to be fire repeatedly. The weapon can self reset, just think of the escapement inside a mechanical clock, as long as there's energy in the gear, the pendulum will swing another way.
As for powering the trap, I got 2 ideas.
1. Dwarf Reset - different trap have different amount of charges it can use before requiring a reload (and even reload before all charge is depleted). Perhaps with a job named "Winding up Trap".
2. Reset by Power Source - Again, use a mechanism gear connected to a power source to continuous re-arm traps. However, instead of every trap needing its own gearing mechanism, the trap themselves should be allowed to transfer energy themselves to other traps nearby (but not to non-trap).
Now a new trap ideas.
Projectile traps triggered by pressure plate.
Example, a crossbow + mechanism trap. When the pressure plate triggers, the crossbow will fire a shot in the direction its pointing at (determine during construction). I have always wanted to build a corridor of flying bolts.
Or maybe a launcher that can launch generic items...
A corridor of flying kitty chunks.