Hi,
1. It depends largely on Personal preference, technical requirements, and also depending on how dynamic a View is. But as a standard SAP uses XML views in the Fiori apps as they are modular and they enforce a clear separation of concerns (UI declaration and handling of business logic). You may base your decision of which view type to use also b referring to the below image showing a comparison between the available types.
2. You can refer to the Fiori Design Guidelines here - https://experience.sap.com/fiori-design/
3. Never load all the required data from the back end on application load, this will just increase the load time of the application when there is high network latency. For loading values in controls like valuehelp, make the necessary call on its valueHelpRequest event.
4. & 5. You can use the Git Repository tool in WebIDE for version management.
6. Follow the design guidelines mentioned in point number 2.
Regards,
Saurabh