Hi, Is the wall solid cement or block?
To answer the rest, metal trowel as well as sponge trowels are typically used. A wet horsehair brush is used to smooth out imperfections, but it is all about what finish you are going for. With acrylic, you are not going to get a heavy texture that you would with traditional stucco topcoating. As far as color, typically for custom colors, an acrylic additive is used added to the corredt base. This is similar to mixing paint. Your supplier will have all those options along with the correct formulas. One or two layers is dependent on the texture you are after, but typically with acrylic, it is done all in one application for most. You can set up a practice area to see how it goes for you experimenting with textures as well as getting familiar with the losseness or dryness of the mix. It is typically applied directly right out of the bucket after the color is mixed in, but can be thinned slightly, again dependent on texture patterns you are after. You can practice on a sheet of plywood as it will adhere to it, then go for it when you feel comfortable. Let me know about the wall you are applying it to as well as any other questions I might be able to answer or what I might have missed.

Here is a link that might be useful: acrylic stucco finishes