How should I layer the ingredients in a taco salad?
While reading your question it sounds like: 'How can I make a salad without the ingredients to touch each other'. So I think what you actually wants is not possible. 

So if you want all of your 3 points to work for, I would suggest you don't make a salad, but serve the chips/cheese separated from the rest of your ingredients. Also, then you can mix the ingredients easily such that your dish does not get plain at the end. 

Maybe it won't look as nice as you want it to look, but it's about taste in the end isn't it! So just:
-Serve the chips/cheese separated from the rest of the salad
-mix the other ingredients such that your dish does not get plain near the end. (I would say, except for the sour cream, you don't want that to be fully mixed with the other ingredients) 
-I also think that serving your chips separately gives you the change to eat them with some  side dishes, like guacamole or a salsa. 

If you really want it to be a salad, you can maybe make smaller portions, so give every person it's own plate. Then there is in total more 'edge' on all plates together to put the chips on, there they will become get less soggy. Also a personal plate will be less 'deep' and so you won't have the problem of getting a plain dish at the end. You can put on the cheese afterwards at the table, so it is not already melted before being served.