which (motor) seals & other components are so most important…??

I hope that this question has not been asked too often :S !? besides my problem with the optics of my car, I am also concerned with the question of which seals (oil seals and others) are most important and affordable … I somehow also have too high oil consumption (where it soups I don’t know but unfortunately I don’t really think it is :S ]) wanted to replace everything like that (if this is possible and not expensive) I’m happy if you could write me any leaks that there are, where it makes sense to replace them and they’re not expensive… if it’s not too much to ask, I’d be happy if you could write to me what else you can replace in the engine to keep it in fire… I’ve somehow decided to take care of the car now (well, there’s really still hope for him)[only thanks to EURER help] ) … … my sister and of course I would be most grateful to you too!!! _____________________________________________________________________________