Very nice models. If this is some of your first work I am really impressed. The paint is really neat and I like the yellow a lot more now you have given if some dirt. I think your Ork forge is going to turn out nice.
The only suggestion I have (not actual advice) is to paint a few different metallic effects for variety. Once you get to bigger models and vehicles you can make large mechanical bits more interesting if you can paint bits gunmetal or bronze or brass or whatever. That's only a personal preference to bring out model detail though.
You're off to a good start.