You need to prove the 800k was in your bank account for 3 months after you received your extension and didn't drop below 400k for the whole year of your extension in order to get your new yearly extension based on 65k per month
Immigration will see your previous years extention and would almost certainly want confirmation that you followed the financial requirements of that extention
As an Italian passport holder you're entitled to a 60 days visa exemption entry into Thailand but you'll need to show your carrier(airline) and possibly Thai Immigration onward travel within 60 days. You can apply for a 30 days extention of stay at your local Thai Immigration Office once you've arrived in the Country