[BigOz]

I build and fly multi-rotors at the moment and have 20+ LiPo batteries hanging around, the safe way to make them ready for disposal when they get a bit dicey is to put them in a bucket of salty water until they have fully discharged.
LiPo are not the right choice for an automotive battery, LiFePO4 lithium iron phosphate (aka LiFe and Lithium Iron) are the common choice although there are lithium cells that contain manganese that also do not show the violent decomposition issues of the older technologies.
BECs and UBECs are used in models to save on using a separate battery for the receiver and other electronics, they regulate the propulsion battery voltage down to the required voltage.
The two types of regulator I'm aware of are linear and switching, linear or shunt regulators which I believe is another term for them, turn the excess into heat and switching do exactly what the name implies, the electronics in them turn the output on and off very quickly to regulate the output.
I've had both kinds of regulator give up in the past on models when the input voltage went over their rated specification and the failure sometimes resulted in the unregulated voltage making it past the regulator.
I've also heard of issues with stacking regulators but that is mostly due to electrical noise issues if I remember correctly.
I've been running a Shorai LiFePO4 battery with no issues for a couple of years now, I did have a few early teething issues but that was a loose terminal and once that was sorted I've had no issues I remember.
Regarding cell balancing, some batteries have internal circuitry to ensure the cells stay balanced, some like my Shorai have a balance port for a supplementary charger but no balancing when charged by the running bike and some have no balancing at all.
An unbalanced battery can become the start of more serious battery issues so I use my balance charger regularly to keep mine in good condition.