I most certainly appreciate the effort and willingness to share your work, you are to be commended for that. Please take my criticism of this as nothing personal and merely a technical point.
This DIY project will do nothing to "stabilize" your system voltage overall. The car's battery is a much bigger capacitor in effect than anything you could build other than adding another battery. It will not add any fuel efficiency and will not keep your voltage from fluctuating.
The only places this circuit could benefit anything is if it is placed on the power supply line right at a device such as a radio. The reason it might benefit there is that the wire run to the device for power has a resistance involved and voltage fluctuations might occur under peak power draw. It could also help filter out a bit of ignition or other electrical noise if placed right at a device. This would mean you would want one of these at every device fed power individually.
There are things already made for this purpose, such as this:
The second one has 1,600,000 mFd whereas as the DIY project here has 13,000 mFd or so. That's 120 times more effective at the purpose for no work and about the same money perhaps.
I have seen studies that show that these capacitors do very little to help with voltage stabilization in any normal use anyway. I cannot find the references at this point but will later it asked.
Even if there is any benefit with the big capacitors, this DIY project's worth is not very high at the very least. I will repeat:
"I most certainly appreciate the effort and willingness to share your work, you are to be commended for that. Please take my criticism of this as nothing personal and merely a technical point."