front of the car, bad smell? Just picked up this 1999 audi a6 beautiful car but with problems (as is trade)

ran a diagnostics with my friends scanner it said cyclinders 1 3 467 are misfiring.
car is now leaking oil all under the engine (soaked)
also there is this bad smell (sometimes)
cars mpg is bad

car runs and gets to point a to b but im worried
engine shakes a lot and throughout the car too
feels like its going to die but then when i hit the gas to accelerate engine is quiet

can i just get some opinons and what you guys think
how costly will this be especially since its a audi
should i keep driving or no?

can i get some ideas and opinions