Dear Yong Peng
You wrote:

> The unique points as I understand are:
>
> 1. the Sangha is (or is supposed to be) a democratic-style assembly.
> 2. there are political entities during Buddha's times which were republics, but built upon a deeply-rooted caste system, i.e. having a ruling caste.

As for (1), I think Sangha cannot be called a democratic institution. Because:
1. At Sangha functions (so-called sanghakammas), the objection of a single monk can overrule the majority vote. (In other words, each monk carries a veto.) So any given function can succeed only if each and everyone present in the assembly gives their agreement.
2. On the other hand, as long as one thinks he is right, he needn't follow the majority; a dhammavaadii (who upholds the dhamma) is a dhammavaadii, whether he is in the minority or in the majority.
3. If a group of monks cannot reach agreement over a controversy, they must live separately.

Of course such regulations cannot be adopted in a lay society.

with metta

Ven. Pandita