No, it isn't mandatory.The choice depends on the current (mA) available on BUS.MyHOMEServer1 consumption is 130mA, if it's localy powered its consumption on bus decrease to 3mA. It's possible use item 346020 like local power supply.
With HOME+PROJECT is not possible to have the backup ( to download on one file the configuration of your installation) of one installation but all your projects details will be always sotred and accessible through the cloud.
Yes, you can manage remotely the deisgn phase of one project through Home + Project web version. But you must be on site and connected the server to manage the configuration through Home + Project app.
To change the language in which to speak to Alexa from the EOS Classe 300 turn on the display and press on settings (wheel) / Amazon Alexa / Alexa speak