DW is up to the arbitration of the group, not the dm's :)
1) yes, cantrips are spells and they are rolled as such.
2) when in doubt, the group decides on what makes sense for everyone at the table. Anyway, yes. If you take prodigy for a level 1 spell, it counts as a level 0 spell/cantrip. However, you can't reduce to cantrip level a spell of level 3 or higher (since both advanced moves reduce its level by 1, a level 3 spell could go as low as level 1, but nothing less).