Buying a 2005 BMW 330xi

I’m looking for any advice on what to look for when shopping for this car. I’ve already test drove it and know I love the handling and performance. I just feel in my element behind the wheel. How many miles should I be looking for? Below 40k? I major decision has been to buy a certified from a BMW dealer or save $2,000-$4,000 or so buying from a random dealer or used car dealer. Does anyone feel the certified tag is just a gimmick to make money? The extended two year warranty matters very little to me. How much should I expect to pay for one with leather and about 30k?

Thanks everyone!