I know that that Proxmox needs 3 nodes to have a Quorum. Does this mean that I need a minimum of 4-node cluster in order to have a proper maintenance (1 host at at time) ?
No, you need 3 nodes for proper maintenance (1 at at time). 2 nodes of a 3 node cluster are quorate, but no further node is allowed to fail.
Generally you need always (n/2)+1 nodes for quorum
