Cover vinyl silk with vinyl Matt

Yes, just key the surface lightly with 120 grit sand paper. You can get a sanding block or an attachment to put on the end of a sanding pole which is much easier work. Cut the sand paper to fit the sanding block or pole sander. Your just taking the sheen or shine off of the vinyl silk. The vinyl Matt will take to the surface much better. “Fresh Look”

Hi. Sanding does help adhesion but dont go too far with it because you might see sanding lines in the finish, 180 might be better. Whenever ive painted matt over silk i have always washed down with sugar soap solution first then clean water. I believe vinyl silk is more likely a finish to have contaminants on its surface, and thats what compromises adhesion of re-coats

Yes it will cover no problem at all but will need several coats to get a vinyl Matt finish

Just a quick sand down needed no need to go over the top

Definitely sand it first but if you really want to be safe you can put a coat of eggshell over the silk first and then matt on top of that. It might seem a little OTT but matt on silk can result in crazing where the matt doesn't adhere properly and if that happens it's a lot of work to put it right.