I used a matte aerosol primer and sealer and went layer by layer in the paint booth.
Sand, prime, sand, prime, sand, prime. Going for that "Impossibly smooth" feel.
It was a challenge to hand-sand the sculpture and retain those crisp, sharp edges. In the end, they got a little rounded.
Due to the softness of MDF, occasionally there would be toolpath artifacts that i wouldn't realize until the finish stage. I used Golden Semi-Gloss Modeling Paste (and my Clipper Card, the perfect applicator) to fill in the cracks inbetween sanding.
When the finish began to resemble the polygons in the graphics software, I knew I was getting somewhere.