Here's a video of the cut: https://youtu.be/ZgANd0I24PM
Some more notes I thought of: To secure the sheet to the spoil board I sprayed the back of the sheet with super 77 adhesive so no holding tabs were necessary. As the steel is conductive it was easy to do a z height measurement across the whole sheet at 100mm intervals to adjust the cut depth along the piece. I was able to use pretty aggressive trochoidal settings. I think it was 20% step length and 25% width. I used 0% oscillation because the bottom of the tool was just cutting soft plywood. After I peeled the finished part off I wiped the adhesive off with mineral spirits. No adhesive remained on the bed.
The part is indeed an enclosure. I've since bent it in a brake and attached it to the bottom of a longboard. I've already made some rims for it but they're 3D printed parts to attach gears to the wheels.
I agree that larger steppers are unnecessary. Before I had worked out proper settings and I was getting violent chatter, the steppers were holding fine, the spindle was just vibrating too much.