I need to see your space and the farric you are planning to put together no way to answer this without context . BTW not IMO a silk fabric for place you put your feet . how about that for pillows instead and a palin fabric that can handle spills and maybe the odd dirty sock.

That design seems all wrong for a patchwork fabric ottoman. Additionally, why destroy that table when the ottoman should probably be made of wood with webbing and batting.

How do you staple to a metal frame? This is how an ottoman is framed.

You likely know most silk is too fragile to use as upholstery unless it has a fused backing/lining.

If you use a metal frame then consider something more like this below.

Remember to measure the height of your table before beginning your project. Is the table at a comfortable height to put your feet up compared to the sofa it will be servicing.? Keep in mind, adding thick foam will add to the overall height.

For practicality and given the multiple needs of the table, consider the pro’s/con’s of leaving as is (especially if using silk and eating there). What about a removable multicoloured/quilted silk runner instead and when using as an ottoman, add a large/square/not too high quilted pillow that matches the runner. When eating, add a washable placemat on top.

If tackling the table per your plan, suggest picking your favorite color comb and use the method you are most comfortable with.

The table looks more than 18" high in the picture. And it'll be higher with cushioning. I'd reduce the height to end up at 18". A latex topper in firm makes a longer lasting cushion pad. Sleep On Latex has them. 3" would work. Pure Green Natural Latex Mattress Topper | SleepOnLatex.com