I would really lean towards a bad Glow Plug Relay and possibly bad glow plugs. You can ohm out the plugs and they should read + or - .2 ohms. Much over 1.0 ohms and you can call it bad and of it reads 0 ohms it s bad as well.
I had exactly the same symtoms about 5 or 6 years ago. It looked like I was spraying the community for bugs. A Glow Plug Relay cured the problem completely.