They are servant, not master.
Unfortunately that 'Friedman rule' belief relies upon there being a fixed amount of money and a one-to-one relationship between money and stuff. There isn't a fixed amount of money. There isn't a one-to-one relationship between money and stuff. Money grows and shrinks depending upon the transaction requirements of the real economy.
A Full Liquidity rule, on the other hand, allows the government sector to adjust its taxation and spending positions and reduce the level of taxation required in a full employment environment.
I'm not sure what you mean by this. The Friedman rule does not assume there is a fixed amount of money -- the rule itself recommends in some circumstances that the central bank should increase the supply of money.
A zero nominal interest rate, while possible, generally requires the central bank to implement a policy of deflation (see [1]). For example, in the US, the long term real interest rate on US treasury securities is 1.74%, so setting the nominal interest rate to 0% would require a deflation at a rate of (1.0174)^-1 per year (~1.71%). While this would eliminate some of the interest earned by "people who have money" it also has the counterbalancing effect of increasing the real value of the money which those people have saved, due to the deflation.
[1] https://en.wikipedia.org/wiki/Friedman_rule