Does the movement get resolved simultaneously?

Yes, all the steps are simultaneously resolved (which might then provoke a variety of triggers).

Can I push something into the void?

No. Since this is forced movement (and not normal unit movement), 'one step' means a single adjacent location. (And 'adjacent location' means an adjacent square in the same region.)

Per card text, artifacts that are carried get pushed as well. So, do held artifacts get blown away from the units carrying them?

Since all of the movement is simultaneous the artifact always shares a location with the unit, so it was never dropped and continues to be carried.

Windblast

Printings