A few companies work together doing stuff like you mentioned but not many are around here. I guess this make more sense in city areas when you deal with different types of property.
I feel like this is only worth doing for select homes or if you own an entire other business with staff. If you do this yourself, you will end up losing money long term.
I am not sure what you mean but DIY services on the side.
Like general repairs you offer for a fee to the person buying the home or? I don't think I would. I don't have the know how to do such a thing myself.