As an art school grad and a former graphic designer, I feel your pain. But as has been said, there's no correct answers here. Someone somewhere will complain. That's the nature of the beast. Do what you want. Jan Rukr's models use a few "simple" diagrams, yet are for the most part easily followed. I have read some instructions that were very simple and yet I couldn't understand them until I talked to someone who explained that I was thinking about them from the wrong frame of reference.
Acceptable model as others have stated- a buildable one.
Appropriate scale or size- entirely subjective. I think that a 4' Republic Attack Gunship is acceptable, my wife: not so much.
What file type is most acceptable? Well, that depends. I personally don't like PDO's much. That's 'cause I mostly use my ancient Mac. But I would also point out that most anyone can open a JPG or PDF. Not the best formats, for high quiality graphics, but the most easily accessible. You decide.
File size- again depends on the subject etc. A 200 meg toaster model is a bit excessive, but All of Jan Rukr's Sulaco? Entirely reasonable.
Detail of directions- gotta be your own judge there, and realize that people will complain.
I've followed your work for some time now. I believe that you said that you make props for a living? Then you know how the creative world works- someone is always going to back bite- those are usually the ones that have the least to talk about. We learned a very VERY important lesson over and over again in my art courses: There is a difference between criticism and critique. There is no reason to be rude when you critique, you never know when the person you blast will blast you back.
Hope this helps, and those of us who do follow your work DO appreciate the work.