Hello lakshmi ambika
I am using moodle version 3.2.2 and the oppiaMobile block is working just fine, maybe i will ask the developer to asnwer your question 1.
2. Solong as the 'Oppia Mobile Export" block is enabled, it will stay visible in editing on mode and editing off mode. After editing and creating your content, Just press the ‘Export to Oppia Package’ button in the right hand column. At the end of the export output page, if it’s all exported successfully, there will be a link to download the course .zip package.
3. Yes, this is possible, make sure you have configured the local server to run django .