This one very much likes the idea of a short term skelebro animated from scrap bones.
Would be an excellent temp followed and possibly bearer.

As far as the ice bridge, an I proved version could have merit, but this one would suggest making it a more advanced spell.
Fine control comes with greater mastery and a higher price.

Also, having build pieces that include sorcery as a prerequisites wouldn’t be the worst idea, if those build pieces are obviously meant to be unnatural.