on new members – a former EC member resigned at the last AGM and was not replaced – do we have to wait until another AGM or ESM to vote more members on?
If the proper procedure was followed at the last AGM, the OC would have decided on the number of seats on the committee. The implication of a vote to decide the numbers required on a strata committee is that a vacancy should be filled as soon as reasonably possible and the committee has the power to do that by asking for volunteers and electing one of them.
Conversely, if there is a vacancy and an owner asks to fill it, then the committee should allow that person to join or present another candidate whom they can elect.
In my building, the chair asks people who are planning not to stand for re-election to resign before the AGM so that the chair and the other committee members can choose their replacement who will then stand a better chance of being re-elected at the next AGM than if it was an open vote. It’s called branch stacking in other areas of politics.
Regarding your definition of “quorum”, that is not the case. The way to avoid tied votes in NSW is to set an odd number of seats on the committee. As described above, a vote on the number of committee members is a legally required part of the election process at an AGM.