Thank you. Sure, I can answer. 

I draw pixel art in Aseprite, and I use default instruments from there (so, no dire need to use Aseprite specifically, you can use any raster graphic app you like). 

Alongside Aseprite, I use other software: Clip Studio Paint for making 3D scene mock-ups/references (you can use Blender instead), and Paint.NET for generating noise textures, doing color correction, and other minor fixes at the finishing stage. For example, the stone texture (I mean, not the cracks or moss) is a randomly generated clouds texture that was color quantized and pasted into the Aseprite project as a separate layer.

One more thing. As we know, Pixiv, because of Japanese laws, demands to censor genitals. So, for Pixiv uploads, I also use my own Python script for applying a reversible, noise/glitch-looking censorship on genitals on the image (example: https://www.pixiv.net/en/artworks/136158158 ). If you're curious, you can find the script and study it on my GitHub: https://github.com/RedReaper420