Consumption when printing is almost secondary. In fact, the printer will ask you to change the cartridges regularly, even if you don't print. A scandal and an ecological shame.
Good question... But if you think you'll be printing regularly, they won't last long, especially in A3, and it will cost you a lot of ink. There are maybe the Epson ecotank printers which can interest you. But I don't know what it's worth...