I've used chalk paint over other paints. I sanded first to remove the sealer and make it smoother.
Yes, you can use chalk paint over paints. I always lightly sand before I paint to remove any imperfections and to scuff up the surface, which makes paint stick better.
Lightly sand and wipe clean and have a go at it.
In deed you can, but sanding always helps. Here is the complete tutorial to help you with an ebook to download. https://bushraslifestyle.com/how-to-chalk-paint-furniture-plus-chalk-paint-recipe
Hope it helps!
Yes! Just sand a bit of there is ant shininess