Well, first of, Archways are a small pain in the butt to make, you can easily over do it 
But, to make your own meshes and textures, I would suggest to take a look at Blender. It’s a free 3D model program and very powerfull.
For texturing, there are multiple solutions, but Photoshop is one of the most known image processing program and has many tutorials available
Here is a topic with free software that can be used for modeling and image processing: