I do a lot of carving in irregular shaped wood, typically well seasoned tree; cherry, pine, holly, and so on.
Holding that piece is a big challenge. It occurred that a vacuum table would be a good solution. Masking off areas of the table with cling film to increase the 'grip' on the job. My initial design is an array of 3mm holes on a 10x10mm grid cut into perspex (just thinking that a 15x15 grid might be better!). Perspex in 2 halves, holes in top, airways in below.

Any thoughts on what would be a suitable hole size, and how close the holes need to be.

I'd put up a dxf of the job if Lee could permit dxf file types (please).