I would like to thank everyone in advance for your help and suggestions!

I am looking to buy a 97-99 S-500 or possibly a 00 S430. This will be my first MB and the one car I have wanted since I was old enough to know what it was. That said, I like to be as educated as possible before I "jump" into it, especially when it is a car purchase. My questions for you are:

What problem areas should I be concerned about?

When I find one I like, are there any characteristics I should look for that would indicate a possible problem?

What routine maintenance is suggested/needed at what miles?

I have been told before that I need to make sure it blows cold air because the condenser (I think) is known to break down. Being that it is located behind the dash, the dash must be removed for repairs and typically costs $3,000 - $3,500. It is problems like that I would like to be aware so I can be prepared should such a situation arise. Again, thank you so much for your help!