Must the formica that now covers my backsplash in my kitchen be removed before installing a new tile backsplash? CAn the tile be adhered directly to the formica? If so what needs to be done to it and what is the best adhesive to use?

Must the formica that now covers my backsplash in my kitchen be removed before installing a new tile backsplash? CAn the tile be adhered directly to the formica? If so what needs to be done to it and what is the best adhesive to use?
If the formica is thoroughly cleaned there shouldn't be a problem.
Who are you buying your tiles from? The may have a recommended or preferred adhesive and I would use their advise.

If it is a high gloss formica you'll need to scuff it up and then vac the dust off it. As for an adhesive just a pre mixed mastic will do fine for tiles that are 6" or less

As for what type of sand paper to use id go with 60 or 80 grit, orbitial sanders work best and in less time

If this were my home I would remove formica & install Hardi-backer (cement board) coated with HPG due to the amount of moisture in the area. After years of tiling I am more inclined to use thinset on most jobs. There is a thinset made for every application.