you're right that in Veyon 4.1 all passwords (also including the LDAP bind password) are stored encrypted in the local configuration. Once you upgrade to Veyon 4.1 and modify the configuration they get encrypted automatically (besides other configuration updates). This means you should save your configuration before upgrading to 4.1 as reverting back to 4.0 will make problems.
Unfortunately Veyon currently is not available for Raspberry Pi (armel/armhf/arm64). You can however build packages on your RPI on your own as described in our README file. We might provide binary packages for RPI in the future as well.
theoretically you can omit the master computer from the configuration with the drawback that auto-discovery of current room will not work. In your case you can enable the setting "Hide local computer" in the Master configuration page in Veyon Configurator. This should hide the master computer while functioning regularly.
If they are on the same network, then try disabling your firewall.
If the connection is successful, try to open ports
Check energy settings to try to solve the sleep mode, it could be an option