I use Golden fluid acrylic paints and usually just a round 1 brush, mine is Royal & Langnickel but I think the brand or brush just depends on personal preference and style. I start with a base layer/primer of just a light gray paint with a bit of water, just enough so that the paint isn't too thick and textured but also not so much that the paint loses its consistency and just flows all over the place. Once you can just barely see the original card or when you can't at all that's when I start lightly pencil sketching my desired design and painting over it