Vetting new workers can occur during the interview process.

It would depend on the particulars of your membership contract. The law would mandate loss of voting rights for fired and leaving workers.

Each worker coop would have a system of internal capital accounts giving each worker a recoupable claim on their investments into the firm. Workers can invest different amounts.

1 worker 1 vote is the principle. Non-voting preferred stock can be free floating property rights as is the case today