Question on tire thread wear for AWD's audi tt
 

I have read somewhere that it is important that all tires almost similar tire wear on AWD cars. I am getting a used 2003 coupe with about 64000km on it. It had 18" rims with series 40 tires but noted the front tires had more wear than the rear tires. Will this affect anything, esp the mechanisms that turn the tires?
Another question is on sludge, I noticed that the engine oil was slightly dark and at a low level. My question is if engine sludge is common, and if the dark colored oil is normal and if it is normal as well for the engine to consume some engine oil? Thanks!!