Let’s start with the black exhaust pipe. All cars that run on unleaded petrol have a sooty black exhaust. The soot will be thicker if the car isn’t tuned properly, but really, the blackness is just a by-product of burning ULP.
Your oil use of about a litre every 1500km is getting towards the top of what is acceptable. Even then, it’s more than this engine should consume. The fact is that all engines use some oil, but it’s usually not enough to require topping up between oil changes. But with your usage rate, you’d need to keep a close eye on the dipstick.
The oil is clearly going somewhere, so check on the ground under where the car is parked each night and look for a pool of oil that suggests the problem is an external leak rather than internal engine wear. From there, have a workshop conduct a compression and leak-down test. The results of this will tell you if the engine’s internal parts are worn and leading to the oil being consumed.
