Thanks for posting here but PLEASE ask simple questions regarding Proxmox VE.
Your topic is really interesting but asking so many questions in one thread - most are not related to Proxmox VE - are most times not that useful here and the majority of the Proxmox experts will not answer due to this.
Templates and cloning works perfectly for me. Do basic checks in your Proxmox VE node/cluster to find the cause of your problems.
If something does not work, you will see clear error messages and log files.