In answer to your first point, yes the tax burden would be 1500 euros pa.
Where a property is empty for part of the year and rented for part of the year, you calculate the notional income for the part of the year the property is empty. The actual rental received is also to be taxed at 25% on gross income without any deductions for expenses or mortgage payments.
The official value is the price declared on purchase.
Yes, your notional rental income would be 1.1% of 300,000 euros, which is 3,300 euros (assuming you don’t rent your property out). This would create a tax liability of 825 euros pa.
Hope this helps.