You've GOT to get some experienced operator-side help on your design and planning team.
What "black start" contingencies are you facing now? How often to do they happen, and what happens to you - your facility - when they do occur? How do you recover now, and what time limits affect you as you recover under what circumstances?
Then ... start thinking: What do you fear? How long a blackout do you think will happen at what regularity? (A 3 hour loss happening once a year is one thing. A 3 day loss happening once every thirty years is another. A 5 minute blackout happening twice a week is a very different problem with a very different solution!)
So, assume you WILL face frequent area blackouts - not just to your plant - and that YOUR facility will be relied on by others to be the first one back up so they can startup safely. See the difference? On the other hand, that may mean you don't need a 5 minute automatic-hands-off immediate restart ability, but DO need to be able to start up in a controlled manner from nothing. A nuke genrating pkant or hospital needs elaborate and expensive auto-start diesels and air-pressurized fuel and oil systems because lives depend on it immediately coming up. That also forces them to buy elaborate auto-switching switchgear duplexed between primary and backup power, plus battery backups and APS systems for all systems that can't even switch from one AC source to another.
You may be able to get by with battery-backed APS systems for your computer, control room, and controllers so they are good for 1/2 hour before AC is restored and so you CAN restart other systems. A small diesel (kilowatt-sized) for building emergency lights and startup pumps like oil. An air-operated starter motor and electric switchable service pumps.