Moving to/E+ card

The best think is to ask the tax office firsts about any tax declaration due. After you are done with taxes make sure you close any bank accounts here and the last step give your E card to your commune and let them know you are going to live in Italy so they remove you from registry.

You go to the commune and hand it back. They also issue you with a form "model 8" which confirms that you are no longer registered, and has your new address in Italy.

If you have been working in Belgium, then tell the tax authorities and file a tax return. As you are leaving relatively early in the year, you are likely to have a very significant tax rebate (all or most of the tax you have paid this year)