I am guessing you have watched laserhackers
Youtube video here -
- he is a regular for me to watch!
I would not recommend this for something mission critical like your startup systems. A bus takes a ton of AMPs for both starting and keeping the bus running. If your alternator failed or started to fail, you would have an immediate dead battery.
Unfortunately, to be able to use these capacitors to power anything other than lights, you would need a whole lot of them. In the video here
- he shows what a large bank looks like and how it can be used with heavy loads along side a solar panel, but the bank you see in the video with the inverter costs more than $1400 to build!
Without the solar power, you might get a few min of use at 400W before the capacitors discharge below the point that the inverter will work. With a solar charge, you could probably get more time, but not reliably I dont think. If you watch toward the end, he talks about why this is not a viable solution yet due to not being able to draw all of the power from each capacitor.
I do however see a huge use for this as an initial load reduction tool for your batteries. Things like fridges, air conditioners and pumps can put a large drain on batteries on initial startup. A capacitor bank would help protect the batteries from sharp pulls of energy, which particularly for lithium iron phosphate, is important. They like long slow even draw of power to be most efficient. When sharp increases in power requirements happen, it can cause the battery to operate less efficiently and in some cases fail.