The next level beyond synthesis involves the components needed for the construction of nanosystems, which are then assembled into a microsystem. Composed of many nanosystems, the cell is nature’s fundamental microsystem. If the first cells were relatively simple, they still required at least 256 protein-coding genes.
If I recall correctly, he is basing this on Venter’s “minimal cell”, although I can’t seem to find a reference to that specific number of genes. I agree with your assessment, it is highly unlikely that we can accurately guess what the first genomes looked like or how they functioned.