Hi. I have a 2.6 too. The 190E's transmission is hydraulic so there is no chip to reprogram. Some changes to the valve body are required for it to start in first gear. You can, however, do this: From a full stop with your foot on the brake move the selector level to '2' then back to 'D' again. Stomp on the gas. Car moves smartly in first then slams into second quite nicely.
Yes, you need to use premium unleaded gas (posted 91 octane at the pump). This is RON 96 / MON 86 gas, commonly called super in the USA.