as in the belief that a decade starts at "0", why isn't there a "Day 0" as the "first" day of every month?

Further, is Sunday or Monday the "Day 0" of the week?

If I owe you 100 dollars, will you be satisfied when I stop at $90.00 when paying you with ten dollar bills, after all, "100" is the beginning of a new decade, isn't it?

"By collecting money for 10 years and spending it for only 6 years,..."

The money collected in the first four years will not be put in the bank for its intended use in future. Most of it will be used to establish the needed bureaucracy. The remainder will be used for some frivolous use.