Each moving part should be its own object. Put each part’s origin in its middle with Object > Set Origin > Origin to Geometry. Start with the model assembled, because the addon remembers where each part belongs the first time you explode.

Yes. Switch Mode to Directional, pick a direction such as plus Z, and the parts slide along it. Parts farther along the direction move farther, so the layers keep their spacing.

Yes. Put each sub-assembly in its own collection and click Add Collection for each one. Every group gets its own center and its own settings, and you can set the order and timing between groups. Assembling plays the order in reverse, so nothing gets stuck on the way back.

No. Pick an empty as the center, select your parts, and click Explode. The addon creates the keyframes, and you can edit them in the Timeline or Graph Editor like any other animation. Prefer to scrub by hand? Switch on Live Slider Mode and drag a slider instead.