Charlie,
1. That is only if the people want such a system. However, if the people do not positions to be held for life and passed on by inheritance they can set up a system where there are no sarrarot, only public servants (Rav Shaul Yisraeli, Havat Binyamin 1,12 p. 92).
2. Abarbanel’s problem with monarchy is that he saw it as always degenerating into tyranny.
3. In the ideal system, which Rambam says will be in place in Mashiach’s time, all these taxes will be paid voluntarily. No need for audits, fines or imprisonment.