you want Bosch W5DC or equivalent. I prefer NGK BP7ES.
Gap should be .024" to .028"
If possible use a torque wrench to install the plugs at 15ftlb with dry threads or 12ftlb with antiseize. Those are lower than book figures but they are safe and I never had a plug fall out.
The rich mixture is gong to be easier to tackle than the oil. Make sure chokes are fully off to start with after that it's checking the carbs are set up right like float level, jet sizes and needle positions are all stock.
The oil burning issue is a matter of degree and it looks worse on the left cylinder. After you get the bike running right you can measure the oil consumption in terms of how much oil you need to add per 1000km. By the way don't top the oil up to the full mark on the dipstick as that tends to make them burn more oil through the engine breather. Set your oil level half way between min and maximum marks. That alone may help.
Last but not least don't go near that garage again. Anyone who worked on an engine including "checking the cylinders" and put back old plugs in that state is not someone you want to do business with. It's not just how black they are but the extreme corrosion suggests the plugs are very old and have not been replaced in a long time.
