Maintaining crispy fried potatoes while cooking with onions and peppers
You probably should keep #3, but use a much higher temperature for the vegetables. 

Non-starchy vegetables contain lots of water. If you shallow fry them at a leisurly pace, their juices flow out and stay in the pan, making everything a bit soft. You also get a bit less grilled-like taste. 

If you saute them instead, you'll end up with dry vegetables. Their juices will evaporate the moment they hit the pan. When you add the potatoes, they will stay crisp. 

You'll have to use a non-nonstick pan for that, it needs temperatures which will destroy a PTFE coating.