to get the first extension you must season the 800k for 2 months before applying then maintain the 800k for 3 months into the extension then never fall below 400k for the rest of the year. When getting a new extension the IO will check that these conditions were met for the first year. If, at any point, the balance in the account fell below these limits then the conditions were not met and the first extension will be void so you'd be back at square one and need a new Non-O to start again. If the conditions were met and, at the same time, there were 12 consecutive monthly international deposits of at least 65k then this can be used for the second extension (and the third etc. if continued).
You obviously have not been to your Immigration Office where your TM30 is filed yet to get their specific list of requirements for your extension. That's a must.
No, it's 800k 2 months before your first extension then start the 65k monthly international transfers at around the same time. Maintain the 800k for the first 3 months of your extension then never fall below 400k for the rest of the year. When your application for your second application is due you will have 12 monthly deposits to switch to the 65k method then you can withdraw the remaining 400k when on your second extension is inked in.