Your missing some initial options on your list;
Do you still need the generator, day and storage tanks?
Most electrical supplies are a lot more stable and down time is reduced. Switching to a higher rated supply line will increasing the stability considerably. One of our sites switched to (I think) 33kva from 11kva and the downtime on the export line is now minimal. A phone call to your provider may be good news and they will have done this locally as part of their ongoing infrastructure improvements.
Also it sounds like you have numerous consumers of diesel on site and it might be more practical, safer and more secure to have one large tank
that everybody draws from to ensure a regular turn over of your wetstock. Simple management levels will ensure you have the same quantity of standby fuel available plus you could potentially reduce your day tank size as well and thereby further reduce your risk of the fuel going off. Lots of flexihose should be avoided as they increase the ability of human error (aka muppet effect!) and people leave them so they will discharge outside of your bund loosing product and causing pollution.
Plus make sure your standby supply is connected to the right systems. I've seen sites with some major standby systems ensuring everything runs but the electric main gate was on the mains supply!